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International Journal of Neuroscience
ISSN: 0020-7454 (Print) 1543-5245 (Online) Journal homepage:
Functional Amyloids: Interrelationship with other
Amyloids and Therapeutic Assessment to Treat
Neurodegenerative Diseases
Sutapa Som Chaudhury & Chitrangada Das Mukhopadhyay
To cite this article: Sutapa Som Chaudhury & Chitrangada Das Mukhopadhyay (2017):
Functional Amyloids: Interrelationship with other Amyloids and Therapeutic Assessment
to Treat Neurodegenerative Diseases, International Journal of Neuroscience, DOI:
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Date: 28 October 2017, At: 05:01
Publisher: Taylor & Francis
Journal: International Journal of Neuroscience
Functional Amyloids: Interrelationship with other Amyloids and Therapeutic
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Assessment to Treat Neurodegenerative Diseases
Sutapa Som Chaudhury1, Chitrangada Das Mukhopadhyay1*
Centre for Healthcare Science and Technology, Indian Institute of Engineering Science and
Technology, Shibpur, PO: Botanic Garden, Dist: Howrah- 711103, West Bengal, India.
*Address Correspondence to:
Dr. Chitrangada Das Mukhopadhayay, Centre for Healthcare Science and Technology, Indian
Institute of Engineering Science and Technology, Shibpur, PO: Botanic Garden, Dist: Howrah711103, West Bengal, India.
Tel: 91-9836544110; 91-9038510873
Fax: (033) 2668-2916
Email: *;
Functional Amyloids: Interrelationship with other Amyloids and Therapeutic
Assessment to Treat Neurodegenerative Diseases
Misfolded β-sheet structures of proteins leading to neurodegenerative diseases like Alzheimer’s (AD) and
Parkinson’s diseases (PD) are in the spotlight since long. However, not much was known about the
functional amyloids till the last decade. Researchers have become increasingly more concerned with the
degree of involvement of these functional amyloids in human physiology. Interestingly, it has been found
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that the human body is exposed to a tremendous systemic amyloid burden, especially, during aging.
Though many findings regarding these functional amyloids come up every day, some questions still
remain unanswered like do these functional amyloids directly involve in the fibrillization of Amyloid
beta (Aβ) 42 peptide or enhance the Aβ42 aggregation rate; whether functional bacterial amyloids
(FuBA) co-localize with the senile plaques of AD or not. A detailed review of the latest status regarding
the interrelationship between functional amyloids, pathogenic amyloids and misfolded prions and
therapeutic assessment of functional amyloids for the treatment of neurodegenerative diseases can help
identify an alternative medication for neurodegeneration. A unique mathematical model is proposed here
for alteration of Aβ42 aggregation kinetics in AD to carve out the future direction of therapeutic
Keywords: Amyloid beta; FuBA; amyloid-burden; mathematical modeling; In-silico model.
Amyloids are insoluble, proteinaceous and fibrillar cross-β-sheet quaternary structures [1] and
amyloidogenesis refers to the aggregation of peptides leading to the synthesis of these amyloids
[2]. Aβ 1-42 has been usually considered as one of the hallmarks of AD pathogenesis, but
recently growing evidence has indicated that a group of amyloids, namely functional amyloids,
may also be associated with normal physiological functions of bacteria to mammals. Functional
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amyloids play a diverse role, ranging from biofilm formation, development of aerial structures to
the regulation of melanin synthesis, scaffolding, epigenetic control, transfer of information and
so on [3]. Both the amyloids are highly resistant to proteolysis and most of them are selfreplicating. Functional amyloids are not harmful to their host, rather play vital roles, e.g., an
amyloid protein activates the Clotting factor XII and helps maintaining hemostasis [4]; human
Pmel17 helps in melanin pigment biosynthesis [5]. The residential bacteria in the human
gastrointestinal (GI) tract produce amyloids that are functional and helpful for their survival in
the host [6]. The gut microbiota play important physiological functions for maintaining
homeostasis in the host body [7,8] and contribute to the proper integrity of the Blood Brain
Barrier (BBB) [9,10].
However, it has been found in recent studies that the human body is exposed to a
tremendous systemic amyloid burden due to the functional amyloid production ability of those
residential bacteria of humans; especially during the ageing-based reorganization of the epithelial
layer of the GI tract and the BBB [11]. Again, Aβ 40 induced increased permeability of BBB
enhance the risk factors in the pathophysiology of AD [12].
All these findings have raised questions whether these functional amyloids co-localize
with the characteristic fibrillar senile plaque of AD or by altering the kinetics of fibrillar
aggregation, functional amyloids worsen the disease condition in neurodegeneration. The whole
scenario becomes more complicated if we consider pathogenic prion protein PrPSc in the same
premise, as it is also a β-amyloid structure and has resemblance with Aβ of AD [13].
Current Food and Drug Administration of USA approved medications for AD are cholinesterase
inhibitors and memantine [14], which offer modest symptomatic improvement only. A partial βsecretase enzyme blocker is now in the center of attraction [15].
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A better understanding of structure function relationship and biogenesis of a diverse kind
of amyloids may lead to the discovery of a novel therapeutic for Alzheimer’s and similar
neurodegenerative diseases.
Structure-function-biogenetic relationship of amyloids:
Structural similarities:
Functional as well as pathogenic amyloids though vary in amino acid sequence, (Table 1)
possess a filamentous and un-branched cross-β-sheet conserved quaternary structure [16-18].
Solid state NMR and PITHIRDS-CT recoupling methods showed that the parallel in-register βsheet topology is omnipresent in pathogenic amyloid structure and also in functional amyloids
like Ure2, Sup35, Rnq1, the RPT domain of functional amyloid Pmel17, [19-21] and so on; with
an exception of Aβ40 (generated in vitro) which is an anti-parallel β-sheet [22]. These parallel
or anti-parallel cross β-sheet structures are employed as low energy structural fold [23] or as a
variant to avoid different strains, a phenomenon common in prions [24, 25].
Generally, the neurodegenerative disease associated pathogenic amyloids may accord
structurally [26] being in the same group. Even FuBA, e.g., HET-s also shows structural
similarity with pathogenic prions having a ‘prion forming domain’ (PFD) at its C-terminus [27].
Functional similarities:
Functional amyloids possess not only a diversified range of occurrence (Table 1) but also serves
in different biological systems, playing crucial roles from biofilm formation to storage vehicles
on the mammalian endocrine system [28]. Whereas, pathogenic amyloids like Aβ42 and PrPSc
are only recruited to hamper the normal physiological functioning [29]. Although, some
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functional similarities between these two types of amyloids bring them on a common platform.
HET-s in Podospora anserine regulates the fungal cell death pathway, namely ‘heterokaryon
incompatibility’ [30], but gets transmitted horizontally from one strain to another just like
infectious prion proteins. Thus, unlikely the structural FuBA – Curli fibers, fungal functional
protein HET-s mimics both prions and amyloidogenesis by transmitting as pathogenic prions and
forming amyloid aggregates [31,32].
The RIP homotypic interaction motif (RHIM) of Receptor interacting kinase 1 (RIP1) and
Receptor interacting kinase 3 (RIP3) (components of necroptosis signaling in mammals),
mediating assembly of these kinases into the amyloid fibrils found to be related to the PFD of
HET-s [33].
URE3 and PSI (yeast prion) also showed corresponds to the prion form of URE2p and Sup35p
(FuBA of Saccharomyces cerevisiae), which are normally soluble proteins, but aggregate in vivo
upon conversion to the prion state [21].
Structural FuBA differs from pathogenic amyloids in terms of biogenesis:
FuBA e.g., Curli fibers of E. coli are synthesized very much similar as the biogenesis of bacterial
flagella [34]. Just as flagellin subunits travel through the flagellar ‘MSP’ ring and attach to the
external end of that ring [35], CsgA secretes out of the cell along with CsgB and CsgF after
transcription from operons - csgDEFG & csgBAC [36]; and get fibrillated with the aid of CsgB
nucleus [37,38]. CsgG pore being an un-gated channel [39] drives the translocation of curli
subunits via the energetics of amyloid subunit folding [40]. Similarly, Chaplin proteins of
Streptomyces coelicolor (ChpA-H) secrete out of the cell and form insoluble layer of 4-6 nm
wide fibrils at air-water interface [41,42] around which all eight Chp proteins generate a bi-
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layered outer coat [43] and help dispersion of spores in wind [44] (Figure 1A and 1B).
Biogenesis of all neurodegenerative amyloids follows almost a common mechanism, in a holistic
way, i.e. the generation of a misfolded protein or peptide which acts as a nucleus to start a chainpolymerization of continuously producing mutated protein units. For AD this nucleating peptide
is the Aβ1-42 [45-47] (Figure 2), in Parkinson’s (PD) this is the α-synuclein [16,48], in
Huntington’s disease this nucleating peptide is the mutated Htt [17,49] and in prion disease, it is
the infectious PrPSc [50] with an additional property to transmit between diseased and healthy
individual [51] (Figure 3).
Harmony in the mechanism of action:
As discussed above, biosynthesis of the senile plaques in AD and in prion diseases show a
synchrony, being more or less similar type of chain elongation reaction. Fascinatingly, fungalfunctional amyloid namely, HET-s imitates a chain elongation reaction like the prion proteins.
The infectious HET-s with the aid of its PFD draws more and more incompatible HET-S and
form fibrillar aggregates [52].
A brief comparison between functional amyloids and pathogenic amyloids is given in Table 2.
Coexistence of Functional and pathogenic amyloids in the human system and its
The structural, functional similarities, as well as the mode of action of different amyloids,
indicate that, if FuBA e.g., Curli, Hydrophobins, increases over time in the GI tract or in another
part of the human body, it will burden the load of similar kind of amyloids in the body. The
indirect effect of bacterial amyloid/endotoxins on CNS mitochondria due to molecular mimicry
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[53] also supports this claim [54,55]. But the question is whether or not the presence of
pathogenic Aβ42 or other neurodegenerative amyloids and the FuBA in the human body at the
same time is just a coincidence. Moreover, it is of great concern if these functional amyloids get
deposited in liver, kidney, colon or any other body parts of human beings [56]. The mechanisms
by which these different types of amyloid are cleared out of the human body, the evolutionary
impact of these functional amyloids in relation with the pathogenic amyloids like Aβ42 and
PrPSc are important areas of ongoing research.
Deposition of FuBA in our body:
Aβ42 peptide and other amyloids are characterized and subsequently defined by amyloid
deposits and non-functioning of a particular organ or total system [57]. In systemic amyloidosis,
amyloidogenic precursor proteins are synthesized at distinct sites from the site of amyloid
deposition [58] and for localized one, the site of amyloidogenic precursor protein synthesis and
deposition are the same [58,59].
Our concern here is whether these FuBA are increasing the burden of amyloid deposition
in the brain with Aβ42, i.e. whether these bacterial amyloids are involved in systemic amyloid
disease. This can be hypothesized that, if FuBAs are involved in systemic amyloidosis, they
would come into the CSF and brain via the circulation and burden the amyloid-load.
Curli, hydrophobins, and gut associated FuBAs might be directly associated with the
breakout of the symptoms of gastrointestinal-amyloidosis [60,61]. The immuno-histochemical
analysis with tissue samples from the patients as well as from a control subject might give an
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answer to this.
FuBA and its impact on Blood-Brain-Barrier permeability:
FuBA may cross the BBB and get full access in the brain hypothalamus if situation favors such
as recurrence of a leaky BBB, altered pattern of gut endothelia and so on. Practically, advanced
stage of AD itself may favor the entry of FuBA in brain interior; as Aβ 1-40 via activation of
JNK/p38 MAPK pathway induces an increase in BBB-permeability [62]. Mutually, the increased
TNFα from uplifting gut microbiota during aging and different cytokines from activated
leukocytes and CNS resident cells in advanced AD exhibit induction of altered paracellular flux
of BBB [63,64]. This results in a reorientation of tight junction protein ‘Occludin’ in a
concentration dependent manner, leading to caspase 3/7 induced apoptosis of brain endothelial
cells [64]. Though there is no direct evidence present for the FuBA to cross the BBB Zipser and
colleagues found significant prothrombin leakage from blood to the CNS in advanced AD
patients as a proof of altered BBB [65]. Increased CSF/plasma protein ratio of albumin and IgG
in AD patients also reflects a leaky BBB [66]. Even much earlier, it was evidenced that; soluble,
circulatory Aβ can cross the BBB and may contribute to the parenchymal amyloid beta
deposition in AD [67]. Thus, in the case of impaired permeability of BBB, FuBA may get an
uncontrolled access in the brain-parenchyma.
Clearance of amyloids from the human system:
Fibrillar β-amyloids, as well as FuBAs, are phagocytosed through the interaction with microglia
[68,69], following cytokines and Reactive Oxygen Species (ROS) generation [70]. The
triggering receptors expressed in myeloid/microglial cells-2 (TREM2) along with membranespanning linker protein TYROBP (DAP12) are employed to phagocytose Aβ40 and Aβ42
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monomeric peptides [71,72].
Complicating the situation bacterial LPS behaves as pro-inflammatory neurotoxins and
down regulates TREM2 and subsequent phagocytosis of monomeric amyloid debris [73].
Talking about infectious prions, after getting access via the M-cells in Peyer’s patch PrPSc
are encountered by the epithelial TLRs [74] and activates microglial cells in the CNS following
priming by astrocytes and even directly binds C1q and factor-H [75]. Once activated, microglial
cells do over-express TLR2, TLR4, and miR146a and up-regulate various markers like TREM2,
SiglecF, CD200R and FCγ receptors in non-classical immune response [76]. After proper
activation, microglia in a similar way as do in AD, activate MHC-II and CR3 receptors, leading
to release of pro-inflammatory cytokines like different interleukins (IL) - IL-1, IL-6, IL-12, and
anti-inflammatory cytokines like IL-4, IL-10, and IL-13 & TGF-β later on [77].
Inhibition of proteasomal degradation by pathogenic amyloids:
In Alzheimer, even 1µM concentration of Aβ42 oligomers suppresses the proteasomal activity
by acting as a competitive inhibitor of the proteolytic subunit of h20S proteasome [78]. This
suggests that Aβ42 oligomers are subjected to h20S proteasomal clearance beside microglial
phagocytosis, though hamper the clearance of other ubiquitin conjugated non-functional proteins
and lead to intra-neuronal deposition of those junk proteins.
The down-regulation of ubiquitin conjugate clearance, i.e. the normal proteasomal
activity is also associated with PD [79], Huntington’s disease [80] and amyotrophic lateral
sclerosis (ALS) [81].
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The Evolutionary link between functional and pathogenic amyloids:
The assessment of the evolutionary link between functional and pathogenic amyloids must be
resolved in determining the interrelationship between these two types of amyloids.
A direct relation between amyloids with similar functions is recognized; e.g, RHIM and
HET-S motifs both serving cell necroptosis are thought to be evolutionarily related [82,83]. On
the other hand, having a C-terminal PFD, HET-s protein shows structural similarity with prions
but differ functionally [84].
Now talking about the evolutionary selection pressure of amyloids we can predict that, if
functional amyloids are under positive evolutionary selection pressure playing an advantageous
role in many organisms; then Aβ42 fibrils, pathogenic prion - PrPSc, α-synuclein and mutant Htt
should be under negative selection pressure serving disadvantageously in the human being.
Instead, researchers argued that Aβ is, in fact, neuroprotective; e.g., Aβ fibrils and plaques sink
down the toxic oligomers or wall off toxic Aβ oligomers [85] and hence prevent formation of
Aβ-oligomer-generated membrane destroying pores and/or subsequent redox reactions [86]. Here
comes the new concept that amyloid structures lie outside the constraints of evolutionary
pressure as these fibrils have not evolved through random DNA mutation rather via physical
interactions and protein folding [87,18]. This implies that there is no conserved primary amino
acid sequence selected through the evolutionary process, to correlate with the conserved
quaternary amyloid structures. Only the forces of protein folding are the deciding factors for
these stable quaternary conformations of any protein.
Carving the way for the improvement of pharmacological therapeutics:
A Mathematical model to determine any alteration in Aβ42 aggregation kinetics:
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A mathematical model proposed combining a bivariate equation and Weibull function as a
chemical concentration model [88] can be used to evaluate the alteration (if any) in the kinetics
of Aβ42 aggregation in the presence of a FuBA at a particular concentration. This equation has
been successfully applied to evaluate the inhibitory effect of organic acids [89] and metals [90]
on the growth of bacteria and the inhibitory effects of some chemical compounds on fibril
aggregation kinetics e.g., inhibitory effect of epigallocatechin-3- gallate on in vitro aggregation
of synthetic insulin [91], the inhibitory effect of mono and Bi flavonoids on Aβ42 amyloid
protein of Alzheimer’s disease [91] and so on. Here, we propose to evaluate the equation for the
analysis of change in the rate of Aβ42 fibril aggregation in the presence of functional amyloid(s);
where the inhibitory compounds of previous studies will be replaced by the functional amyloid.
The data which would be analyzed by this mathematical equation could be obtained by
performing an in vitro experiment where the aggregation rate of Aβ42 in the presence of a FuBA
(synthetic) at a particular concentration and conformation would be measured by ThT
fluorescence [91] intensity at an excitation wavelength of 450 nm and an emission wavelength
range of 460 nm to 520 nm. The mathematical equation is as follows:
X= Xm. / [1+ exp{2+(4vm. (λ.-t)/Xm.)}]
Xm. = Xm {1-Kx [1-exp (-ln2 (C/mx)^ax)]}
vm. = vm {1-Kv [1-exp (-ln2 (C/mv)^av)]}
. =  {1+K [1-exp (-ln2 (C/m)^a)]}
Where Xm is the aggregation growth at its maximum limit, vm is the maximum
aggregation rate, λ is the lag phase and C is the concentration of FuBA with a particular
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conformation. The meanings of other symbols and their corresponding units are summarized in
Table 3. The dependent variable of response or time dependent signal (X) is to detect amyloid
protein aggregation by ThT fluorescence intensity at 460 nm to 520 nm in the in vitro assay. It is
to be noted that, different FuBA, other than that of GI tract when present in vivo may contribute
to the rate of aggregation of Aβ42 fibrils; in such case, this equation might follow an exponential
logarithm and the final kinetic equation would be changed according to the respective variable
Development of an in silico model to predict colocalization of pathogenic and nonpathogenic
amyloids in the human system:
It can be hypothesized that to alter the kinetics of Aβ42 fibrillization, gut microflora derived
FuBA would employ a co-localization mechanism. To provide evidence, beside the classical
Immuno-histochemical double labeling experiments [92] one new-age scientific approach will be
to generate an in silico model. In this computer modeling [93] a vast sample data from AD
patients would be analyzed, followed by wet lab experimental validation through latest
molecular biological techniques.
Similarly, Immune-precipitation of blood and CSF samples from AD patients with
primary antibodies [94] against the functional amyloids would not be sufficient to confirm the
increase of amyloid burden with age; because other variable parameters like the physiological
condition of the gut, the presence of other kinds of amyloids are to be analyzed at the same time.
This can only be done with an in silico model supplemented with the immense data from AD
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Such a clinical trial simulation tool has been developed with the aid of a standard
database, model development, and evaluation, and was approved by FDA and EMA in 2013
[95]. This was proved to be helpful for the detection of disease progression based on a
longitudinal AD assessment scale-cognitive sub-scale scores, as well as beneficial for the clinical
phase trials for drug evaluation and appeared stretchier than final phase trials of Alzheimer’s
drugs, considering the different non-linear effects shown by the drugs [95].
Throwing light on future therapeutics:
Treatment with functional amyloid against β-amyloid:
When it is of concern whether FuBA enhances pro-inflammatory responses in neurodegeneration
it comes as a surprise that, FuBA like Curli can act as an immuno-modulator elevating antiinflammatory IL10 level via TLR2 activation when only gut epithelia are impaired but strictly
not in the case of an intact gut epithelial barrier [10]. Oppong and colleagues showed that, when
Curli fibers were introduced through intraperitoneal injection and allowed to interact directly
with gut lamina propia, the expression level of IL10 got increased [10]. The reason behind this
may be some alteration in the activation of the adapter molecule MYD88 or TIRAP/MAL
leading to switching from the downstream severe pro-inflammatory pathway to healing antiinflammatory response [96]. Thus, if Curli fibers were targeted to the CNS with the aid of tagged
nano-particles [97] increased level of anti-inflammatory IL10 may help to switch M2 microglial
phenotype from pro-inflammatory phenotype M1 [98] and thus help reduce neuroinflammation.
In fact, IL4 and IL10 treatment have been tested in vitro and in vivo and proved to improve
pivotal neuroinflammation in AD [99,100].
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Inhibition of Necrosome and inflammasome:
Pro-inflammatory cytokines particularly TNFα induced necroptosis and subsequent loss of a
subset of neurons in case of increased amyloid burden are the major pathogenesis of
neurodegenerative diseases [101]. Necroptosis, a programmed necrosis mediated by necrosome
complex [102,101] gets activated via the de-ubiquitination of RIP1 by Cylindromatosis (CYLD)
[103]. Reportedly, targeted inhibition of RIP1 kinase by necrostatin-1 has shown to give
protection from neuronal damage in animal models of brain injury, stroke and ALS [104,105].
Importantly, necrosome complex formation via RHIM domain interaction between RIP1 and
RIP3 leads to β-amyloid like complex formation [33] as a part of this necrosome complex and
thus targeted inhibition of RIP1 or RIP3 would be an indirect approach of treating β-amyloidosis
like AD, targeting other β-amyloid than Aβ42 directly. Similarly, the NLRP3 inflammasome
complex that serves a necrotic function in mammals via pro-inflammatory cytokines IL1β and
IL18 response [106] is reported to get activated by all kinds of amyloids including Aβ, serum
amyloid A, islet amyloid peptide, prions and functional amyloid – Curli [107,108]. Therefore,
hanging up the NLRP3 inflammasome particularly at IL1β signaling level using an IL1 receptor
antagonist, may result in the reduction of the pro-inflammatory pathogenesis of AD.
Controlled inhibition of JNK/ P38 MAPK pathway:
In brain diseases, cancer, rheumatoid arthritis and such many more diseases JNK/p38MAPK
pathway is being talked about and explained as a good therapeutic target since decades. It was
reported that p38MAPK inhibition can reverse the effect of Aβ42 induced boost in TNFα and
IL-1β level and subsequent synaptic dysfunction in mice-hippocampus [109], but the mechanism
was not known. Later on, in 2010, it was revealed that, scrambled Aβ peptide induced increase in
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cytokines triggers JNK/p38MAPK signaling pathway that leads to apoptosis of brain endothelial
cells (BEC) and consequent reorganization of BBB’s tight junction protein Occludin [62]. Also,
Lopez-Ramirez and colleagues mentioned the inhibition of the JNK pathway as a therapeutic
measure of BBB breakdown, adding the role of caspases 3/7 and caspase 9 in BBB impairment
Thereby, talking about the dual presence of Aβ42 as well as FuBA simultaneously in a
patient, JNK/p38MAPK pathway and/or caspase 3/7/9 seems to be an appropriate therapeutic
target to treat the critical neuroinflammatory condition.
The Role of Chaperones:
This is only the copious chaperone molecules which congregate all the neurodegenerative
diseases including AD, PD and prion diseases at a common terminus.
Evans and colleagues earlier reported that recombinant Hsp70/40 and Hsp90 chaperone
molecules block Aβ self-assembly causing structural changes in oligomers but remain unaffected
against fibrils [110].
Hsp70/Ssa3 isoform (Ssa1-4 are four cytosolic Hsp isoforms in S. cerevisiae) lowers αsynuclein-toxicity in PD via modulating autophagy [111] and Hsp90 binds and prevents the
aggregation of α-synuclein oligomers in an ATP-independent manner [112].
For mammalian prion diseases, Hsp70 either promotes degradation of PrPSc conformers
or protects against PrP-neurotoxicity [113]. Also, an up-regulation of Hsp90 was observed
previously in murine models of Bovine Spongiform Encephalopathies (BSE) [114].
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Interestingly, the role of Hsp70 and Hsp90 is eminent not only in mammalian pathogenic
amyloids but also in FuBA e.g., in yeast prion propagation. A current report in this field has
stated that the C-terminal MEEVD pentapeptide motif of Hsp90 is indispensable for URE3 prion
stability of S. cerevisiae [115] (URE3 is a prion form of native protein URE2).
Taking into account the diversified role of Hsp70-Hsp90 in the response of amyloids, this
Hsp70-Hsp90 dual machinery might be targeted for combination therapeutics against prion and
Aβ42 and/or prion, FuBA, and Aβ42.
Restoring proteasomal activity by pyrazolone containing small molecules or proteasome
activator and/or de-ubiquitinating enzyme inhibitor:
As discussed above, competitive inhibition of 20S proteasome by Aβ42, α-synuclein and mutant
Htt in AD, PD and Huntington’s disease respectively leads to accumulation of ubiquitin
conjugates in neurons. Thereby, small molecules that act as the activator of proteasomal complex
and increase the turnover rate of proteasome could be a therapeutic measure. Pyrazolone small
molecules were shown to enhance proteasomal activity and significantly attenuate disease
progression in the case of ALS [81]. An in vitro enhanced clearance of mutated Htt was reported
by over-expressing proteasome activator subunit PA28γ [116]. Also, the molecules that inhibit
USP14, a proteasome associated de-ubiquitinating enzyme can activate proteasomal degradation
[117] and thus can be another therapeutic target.
Vagotomy – a therapeutic approach for FuBA affected neurodegeneration:
PD is hypothesized to start in the GI tract and spread to the brain through the vagus nerve [118].
Recently, the presence of Lewy body in the GI tract of PD patients prior to their motor neuron
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dysfunction was detected [119]. Also, Helicobacter pylori infection in the stomach has been
proven to worsen the motor problems in PD [120]. Vagotomy i.e. a complete cutoff of vagus
nerve was proved to be a successful therapeutic measure in experimental volunteers suffering
from PD [118].
Here in this review, as we are assessing the role of FuBA of gut microbes in AD,
vagotomy can be a promising therapeutic target. We are to detect whether vagotomy can prevent
the enhancement of Aβ fibrillization kinetic in presence of FuBA.
Concluding Remarks:
The amyloid proteins in the neurodegenerative disease like Alzheimer’s (Aβ42) drew the
attention of researchers since long as compared to the widespread functional amyloids; but it is
not a truthful idea that amyloids are always associated with diseases; rather it can be allied with
function or disease. The functional amyloid of gut microflora may enhance inflammatory
symptoms and subsequent disease progression of Alzheimer’s. Here in this review, we have tried
to portray the pathophysiology of AD in presence of FuBA and increased amyloid burden; figure
out the factors that may favor this dual presence of Aβ and FuBA in the brain hypothalamus. As,
for example, increased level of TNFα during sepsis increases the permeability of the BBB and
even Aβ40 itself down-regulate the tight junction protein ‘Occludin’ of the BBB and thus make
the BBB more permeable. If such dual presence of Aβ42 and FuBA (and/or prion) had arisen,
this would affect the downstream clearance of Aβ42 oligomers/monomers in Alzheimer patients.
Aβ fibers generated by the oligomerization of Aβ42 monomers are cleared out by Toll Like
Receptor 2 (TLR2) signaling pathway. The downstream redox reactions producing ROS and proinflammatory cytokines are mainly responsible for the inflammation and symptomatic
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neurodegeneration in Alzheimer’s disease. Moreover, the ROS generated in TLR2 signaling
pathway down-regulate the Aβ42 monomer clearance via TREM2, and ultimately facilitates
senile plaque formation in AD. The whole scenario could be more complicated and might even
do so with the increase of amyloid load in our system with age through the influence of FuBA in
gut microflora. Bacterial LPS and FuBA allegedly down-regulate TREM2 robustly and therefore
the phagocytic clearance of monomeric amyloid debris (Figure 2).
Though we are still left with the answer whether these FuBA could cross the blood brain
barrier; with the aid of tracer 70 KD FITC-dextran it has been shown that Aβ40 can induce a
marked increase in hCMEC/D3 cell (BBB model) permeability via activation of JNK/p38
MAPK pathway, when incubated with scrambled Aβ40 peptide at a non-cytotoxic dose [62].
This, in turn, may dig the path for the entry of FuBA in the hypothalamus, crossing the BBB.
Interestingly, besides these negative roles of FuBA during aging, FuBA specifically Curli from
gut microflora can act as an immunomodulator in hapten (TNBS) induced colitis in experimental
mice models but not in the case of intact gut epithelial barrier [10]. Even, a crosstalk between gut
microbiota and the brain started during gestation, leads to the proper expression of tight junction
protein of the BBB and therefore the subsequent development of an intact and functional bloodbrain-barrier [9]. Thus, whether these FuBA would behave as immunomodulator or chronic
neuroinflammatory response developer is a dependent function of physiological background, i.e.
the status of gut epithelia, the presence of FuBA in the brain and beyond the gut, increasing
amyloid burden with age etc. and is subjected to estimation by in silico modeling.
Functional amyloids hence call more concern in pharmacological investigations of
neurodegenerative diseases. Establishment of an alternative medication of neurodegenerative
diseases nowadays in the center of attraction as the current symptomatic treatment is already
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ringing a bell of alarm.
The points discussed in this review article regarding treatment with functional amyloid
against β-amyloid, inhibition of necrosome, inflammasome and vagotomy can be helpful in this
aspect. A combination of the therapies proposed here may appear as a successful new age
alternative medication for neurodegeneration, after passing clinical phase trials.
Validation of the mathematical model and other experimental methods discussed above
will shed light on the unrevealed field of amyloid beta fibrillization kinetics in presence of
Conflicts of Interest:
The authors report no conflict of interest.
This research did not receive any specific grant from funding agencies in the public, commercial,
or not-for-profit sectors.
We thank Mr. Bhuban Ruidas (Indian Institute of Engineering Science and Technology, Shibpur)
for proof reading the manuscript and for his valuable suggestions.
Authorship Contributions:
Wrote or contributed to the writing of the manuscript: Som Chaudhury, Das Mukhopadhayay.
Graphics and drawings: Som Chaudhury.
Math model hypothesis proposed: Som Chaudhury.
Downloaded by [University of Florida] at 05:01 28 October 2017
Math model hypothesis evaluated: Das Mukhopadhayay.
[1] Maurer-Stroh S, Debulpaep M, Kuemmerer N, et al. Exploring the sequence determinants of
amyloid structure using position-specific scoring matrices. Nature methods. 2010;7(3):237-242.
[2] Usnarska-Zubkiewicz L, Hołojda J, Kuliczkowski K. AL Amyloidosis (Amyloidosis
Antibody Light). Part 1. Definition, Classification, Amyloid Structure, Development and
Etiopathogenesis of AL Amyloidosis. Clin Exp Med. 2011;20(5):647-652.
[3] Maury CP. The emerging concept of functional amyloid. J Intern Med. 2009;265(3):329-334.
[4] Fowler DM, Koulov AV, Balch WE, et al. Functional amyloid–from bacteria to humans.
Trends Biochem Sci. 2007;32(5):217-224.
[5] Jiang Z, Lee JC. Lysophospholipid-containing membranes modulate the fibril formation of
the repeat domain of a human functional amyloid, pmel17. J Mol Biol. 2014;426(24):4074-4086.
[6] Syed AK, Boles BR. Fold modulating function: bacterial toxins to functional amyloids. Front
Microbiol. 2014;5:401.
[7] Sommer F, Bäckhed F. The gut microbiota—masters of host development and physiology.
Nat Rev Microbiol. 2013;11(4):227-238.
[8] Lin CS, Chang CJ, Lu CC, et al. Impact of the gut microbiota, prebiotics, and probiotics on
human health and disease. Biomed J. 2014;37(5):259.
[9] Braniste V, Al-Asmakh M, Kowal C, et al. The gut microbiota influences blood-brain barrier
Downloaded by [University of Florida] at 05:01 28 October 2017
permeability in mice. Sci Transl Med. 2014;6(263): 263ra158-263ra158.
[10] Oppong GO, Rapsinski GJ, Tursi SA, et al. Biofilm-associated bacterial amyloids dampen
inflammation in the gut: oral treatment with curli fibres reduces the severity of hapten-induced
colitis in mice. NPJ Biofilms Microbiomes. 2015;1:15019.
[11] Hill JM, Lukiw WJ. Microbial-generated amyloids and Alzheimer's disease (AD). Front
Aging Neurosci. 2015;7:9.
[12] Hartz AM, Bauer B, Soldner EL, et al. Amyloid-β contributes to blood–brain barrier leakage
in transgenic human amyloid precursor protein mice and in humans with cerebral amyloid
angiopathy. Stroke. 2012;43(2):514-523.
[13] Tycko R. Solid state NMR studies of amyloid fibril structure. Annu Rev Phys Chem.
[14] Wattmo C, Minthon L, Wallin ÅK. Mild versus moderate stages of Alzheimer's disease:
three-year outcomes in a routine clinical setting of cholinesterase inhibitor therapy. Alzheimers
Res Ther. 2016;8(1):1.
[15] Halima SB, Mishra S, Raja KM, et al. Specific Inhibition of β-Secretase Processing of the
Alzheimer Disease Amyloid Precursor Protein. Cell Rep. 2016;14(9):2127-2141.
[16] Volpicelli-Daley LA, Luk KC, Patel TP, et al. Exogenous α-synuclein fibrils induce Lewy
body pathology leading to synaptic dysfunction and neuron death. Neuron. 2011;72(1):57-71.
[17] Trepte P, Strempel N, Wanker EE. Spontaneous self-assembly of pathogenic huntingtin
exon 1 protein into amyloid structures. Essays Biochem. 2014;56:167-180.
[18] Rapsinski GJ, Wynosky-Dolfi MA, Oppong GO, et al. Toll-like receptor 2 and NLRP3
Downloaded by [University of Florida] at 05:01 28 October 2017
cooperate to recognize a functional bacterial amyloid, curli. Infect Immun. 2015;83(2):693-701.
[19] McGlinchey RP, Shewmaker F, McPhie P, et al. The repeat domain of the melanosome
fibril protein Pmel17 forms the amyloid core promoting melanin synthesis. Proc Natl Acad Sci U
S A. 2009;106(33):13731-13736.
[20] McGlinchey RP, Shewmaker F, Hu KN, et al. Repeat domains of melanosome matrix
protein Pmel17 orthologs form amyloid fibrils at the acidic melanosomal pH. J Biol Chem.
[21] Wickner RB, Shewmaker F, Edskes H, et al. Prion amyloid structure explains templating:
how proteins can be genes. FEMS Yeast Res. 2010;10(8):980-991.
[22] Perl DP. Neuropathology of Alzheimer's disease. Mt Sinai J Med. 2010;77(1):32-42.
[23] Shewmaker F, McGlinchey RP, Wickner RB. Structural insights into functional and
pathological amyloid. J Biol Chem. 2011;286(19):16533-16540.
[24] Shewmaker F, McGlinchey RP, Thurber KR, et al. The functional curli amyloid is not based
on in-register parallel β-sheet structure. J Biol Chem. 2009;284(37):25065-25076.
[25] Gendoo DM, Harrison PM. Origins and evolution of the HET-s prion-forming protein:
searching for other amyloid-forming solenoids. PloS One. 2011;6(11):e27342.
[26] Knowles TP, Vendruscolo M, Dobson CM. The amyloid state and its association with
protein misfolding diseases. Nat Rev Mol Cell Biol. 2014;15(6):384-396.
[27] Wasmer C, Lange A, Van Melckebeke H, et al. Amyloid fibrils of the HET-s (218–289)
prion form a β solenoid with a triangular hydrophobic core. Science. 2008;319(5869):1523-1526.
[28] Maji SK, Perrin MH, Sawaya MR, et al. Functional amyloids as natural storage of peptide
Downloaded by [University of Florida] at 05:01 28 October 2017
hormones in pituitary secretory granules. Science. 2009;325(5938):328-332.
[29] Bjorndahl TC, Zhou GP, Liu X, et al. Detailed biophysical characterization of the acidinduced PrPc to PrPβ conversion process. Biochemistry. 2011;50(7):1162-1173.
[30] Saupe SJ. The [Het-s] prion of Podospora anserina and its role in heterokaryon
incompatibility. Semin Cell Dev Biol. 2011;22(5): 460-468.
[31] Van Melckebeke H, Wasmer C, Lange A, et al. Atomic-resolution three-dimensional
structure of HET-s (218− 289) amyloid fibrils by solid-state NMR spectroscopy. J Am Chem
Soc. 2010;132(39):13765-13775.
[32] Seuring C, Greenwald J, Wasmer C, et al. The mechanism of toxicity in HET-S/HET-s
prion incompatibility. PLoS Biol. 2012;10(12):e1001451.
[33] Li J, McQuade T, Siemer AB, et al. The RIP1/RIP3 necrosome forms a functional amyloid
signaling complex required for programmed necrosis. Cell. 2012;150(2):339-350.
[34] Duque E, de la Torre J, Bernal P, et al. Identification of reciprocal adhesion genes in
pathogenic and non‐pathogenic Pseudomonas. Environ Microbiol. 2013;15(1):36-48.
[35] Willey JM, Sherwood LM, Woolverton CJ. Prescott, Harley, and Klein’s Microbiology. 7th
ed. New York (NY): McGraw Hill Higher Education; 2008. Chapter 3, Prokaryotic Cell
Structure and Function; p. 66-70.
[36] Blanco LP, Evans ML, Smith DR, et al. Diversity, biogenesis and function of microbial
amyloids. Trends Microbiol. 2012;20(2):66-73.
Downloaded by [University of Florida] at 05:01 28 October 2017
[37] Cao B, Zhao Y, Kou Y, et al. Structure of the nonameric bacterial amyloid secretion
channel. Proc Natl Acad Sci U S A. 2014;111(50):E5439-E5444.
[38] Evans ML, Chorell E, Taylor JD, et al. The bacterial curli system possesses a potent and
selective inhibitor of amyloid formation. Mol Cell. 2015;57(3):445-455.
[39] Taylor JD, Zhou Y, Salgado PS, et al. Atomic resolution insights into curli fiber biogenesis.
Structure. 2011;19(9):1307-1316.
[40] Taylor JD, Matthews SJ. New insight into the molecular control of bacterial functional
amyloids. Front Cell Infect Microbiol. 2015;5:33.
[41] Duong A, Capstick DS, Di Berardo C, et al. Aerial development in Streptomyces coelicolor
requires sortase activity. Mol Microbiol. 2012;83(5):992-1005.
[42] Sawyer EB, Claessen D, Haas M, et al. The assembly of individual chaplin peptides from
Streptomyces coelicolor into functional amyloid fibrils. PLoS One. 2011;6(4):e18839.
[43] Bokhove M, Claessen D, de Jong W, et al. Chaplins of Streptomyces coelicolor selfassemble into two distinct functional amyloids. J Struct Biol. 2013;184(2):301-309.
[44] Ekkers DM, Claessen D, Galli F, et al. Surface modification using interfacial assembly of
the Streptomyces chaplin proteins. Appl Microbiol Biotechnol. 2014;98(10):4491-4501.
[45] Roychaudhuri R, Yang M, Hoshi MM, et al. Amyloid β-protein assembly and Alzheimer
disease. J Biol Chem. 2009;284(8):4749-4753.
[46] Tay WM, Huang D, Rosenberry TL, et al. The Alzheimer's amyloid-β (1–42) peptide forms
Downloaded by [University of Florida] at 05:01 28 October 2017
off-pathway oligomers and fibrils that are distinguished structurally by intermolecular
organization. J Mol Biol. 2013;425(14):2494-2508.
[47] Gautam V, D’Avanzo C, Berezovska O, et al. Synaptotagmins interact with APP and
promote Aβ generation. Mol Neurodegener. 2015;10(1):1.
[48] Gröger A, Kolb R, Schäfer R, et al. Dopamine reduction in the substantia nigra of
Parkinson's disease patients confirmed by in vivo magnetic resonance spectroscopic imaging.
PloS One. 2014;9(1):e84081.
[49] Cortes CJ, La Spada AR. The many faces of autophagy dysfunction in Huntington's disease:
from mechanism to therapy. Drug Discov Today. 2014;19(7):963-971.
[50] Singh J, Udgaonkar JB. Molecular mechanism of the misfolding and oligomerization of the
prion protein: current understanding and its implications. Biochemistry. 2015;54(29):4431-4442.
[51] Biasini E, Turnbaugh JA, Unterberger U, et al. Prion protein at the crossroads of physiology
and disease. Trends Neurosci. 2012;35(2):92-103.
[52] Baiesi M, Seno F, Trovato A. Fibril elongation mechanisms of HET‐s prion‐forming
domain: Topological evidence for growth polarity. Proteins: Structure, Function, and
Bioinformatics. 2011;79(11):3067-3081.
[53] Kitani T, Kami D, Kawasaki T, et al. Direct human mitochondrial transfer: a novel concept
based on the endosymbiotic theory. Transplantation proceedings 2014;46(4):1233-1236.
[54] Via A, Uyar B, Brun C, et al. How pathogens use linear motifs to perturb host cell networks.
Trends Biochem Sci. 2015;40(1):36-48.
[55] Zhao Y, Dua P, Lukiw WJ. Microbial sources of amyloid and relevance to amyloidogenesis
Downloaded by [University of Florida] at 05:01 28 October 2017
and Alzheimer’s disease (AD). J Alzheimers Dis Parkinsonism. 2015;5(1):177.
[56] Mormino EC, Smiljic A, Hayenga AO, et al. Relationships between beta-amyloid and
functional connectivity in different components of the default mode network in aging. Cereb
Cortex. 2011;21: 2399-2407.
[57] Sipe JD, Benson MD, Buxbaum JN, et al. Amyloid fibril protein nomenclature: 2010
recommendations from the nomenclature committee of the International Society of Amyloidosis.
Amyloid. 2010;17(3-4):101-104.
[58] Perfetto F, Moggi-Pignone A, Livi R, et al. Systemic amyloidosis: a challenge for the
rheumatologist. Nat Rev Rheumatol. 2010;6(7):417-429.
[59] Shikama Y, Kitazawa JI, Yagihashi N, et al. Localized amyloidosis at the site of repeated
insulin injection in a diabetic patient. Intern Med. 2010;49(5):397-401.
[60] Sattianayagam PT, Hawkins PN, Gillmore JD. Systemic amyloidosis and the
gastrointestinal tract. Nat Rev Gastroenterol Hepatol. 2009;6(10):608-617.
[61] Madsen LG, Gimsing P, Schiødt FV. Primary (AL) amyloidosis with gastrointestinal
involvement. Scand J Gastroenterol. 2009;44(6):708-711.
[62] Tai LM, Holloway KA, Male DK, et al. Amyloid‐β‐induced occludin down‐regulation and
increased permeability in human brain endothelial cells is mediated by MAPK activation. J Cell
Mol Med. 2010;14(5):1101-1112.
[63] Tsao N, Hsu HP, Wu CM, et al. Tumour necrosis factor-α causes an increase in blood-brain
barrier permeability during sepsis. J Med Microbiol. 2001;50(9):812-821.
Downloaded by [University of Florida] at 05:01 28 October 2017
[64] Lopez-Ramirez MA, Fischer R, Torres-Badillo CC, et al. Role of caspases in cytokineinduced barrier breakdown in human brain endothelial cells. J Immunol. 2012;189(6):3130-3139.
[65] Zipser BD, Johanson CE, Gonzalez L, et al. Microvascular injury and blood–brain barrier
leakage in Alzheimer's disease. Neurobiol Aging. 2007;28(7):977-986.
[66] Matsumoto Y, Yanase D, Noguchi-Shinohara M, et al. Blood-brain barrier permeability
correlates with medial temporal lobe atrophy but not with amyloid-β protein transport across the
blood-brain barrier in Alzheimer’s disease. Dement Geriatr Cogn Disord. 2007;23(4):241-245.
[67] Lauer D, Reichenbach A, Birkenmeier G. α2-Macroglobulin-mediated degradation of
amyloid β1–42: a mechanism to enhance amyloid β catabolism. Exp Neurol. 2001;167(2):385392.
[68] Liu S, Liu Y, Hao W, et al. TLR2 is a primary receptor for Alzheimer’s amyloid β peptide
to trigger neuroinflammatory activation. J Immunol. 2012;188(3):1098-1107.
[69] Schwartz K, Boles BR. Microbial amyloids–functions and interactions within the host. Curr
opin microbiol. 2013;16(1):93-99.
[70] Glass CK, Saijo K, Winner B, et al. Mechanisms underlying inflammation in
neurodegeneration. Cell. 2010;140(6):918-934.
[71] Melchior B, Garcia AE, Hsiung BK, et al. Dual induction of TREM2 and tolerance-related
transcript, Tmem176b, in amyloid transgenic mice: implications for vaccine-based therapies for
Alzheimer's disease. ASN Neuro. 2010;2(3):AN20100010.
[72] Yaghmoor F, Noorsaeed A, Alsaggaf S, et al. The role of TREM2 in Alzheimer’s disease
and other neurological disorders. J Alzheimers Dis Parkinsonism. 2014;4(5).
Downloaded by [University of Florida] at 05:01 28 October 2017
[73] Zhao Y, Lukiw WJ. Microbiome-generated amyloid and potential impact on
amyloidogenesis in Alzheimer’s disease (AD). J Nat Sci. 2015;1(7).
[74] Zabel MD, Avery AC. Prions—Not Your Immunologist’s Pathogen. PLoS Pathog.
[75] Bradford BM, Mabbott NA. Prion disease and the innate immune system. Viruses.
[76] Lunnon K, Teeling JL, Tutt AL, et al. Systemic inflammation modulates Fc receptor
expression on microglia during chronic neurodegeneration. J Immunol. 2011;186(12):7215-7224.
[77] Tu J, Chen B, Yang L, et al. Amyloid-β Activates Microglia and Regulates Protein
Expression in a Manner Similar to Prions. J Mol Neurosci. 2015;56(2):509-518.
[78] Zhao X, Yang J. Amyloid-β peptide is a substrate of the human 20S proteasome. ACS Chem
Neurosci. 2010;1(10):655-660.
[79] Nonaka T, Hasegawa M. A cellular model to monitor proteasome dysfunction by αsynuclein. Biochemistry. 2009;48(33):8014-8022.
[80] Hipp MS, Patel CN, Bersuker K, et al. Indirect inhibition of 26S proteasome activity in a
cellular model of Huntington’s disease. J Cell Biol. 2012;196(5):573-587.
[81] Trippier PC, Zhao KT, Fox SG, et al. Proteasome activation is a mechanism for pyrazolone
small molecules displaying therapeutic potential in amyotrophic lateral sclerosis. ACS Chem
Neurosci. 2014;5(9):823-829.
Downloaded by [University of Florida] at 05:01 28 October 2017
[82] Kajava AV, Klopffleisch K, Chen S, et al. Evolutionary link between metazoan RHIM motif
and prion-forming domain of fungal heterokaryon incompatibility factor HET-s/HET-s. Sci Rep.
[83] Daskalov A, Dyrka W, Saupe SJ. Theme and variations: evolutionary diversification of the
HET-s functional amyloid motif. Sci Rep. 2015;5.
[84] Greenwald J, Riek R. Biology of amyloid: structure, function, and regulation. Structure.
[85] Greenough MA, Camakaris J, Bush AI. Metal dyshomeostasis and oxidative stress in
Alzheimer’s disease. Neurochem Int. 2013;62(5):540-555.
[86] Selkoe DJ. Toward a comprehensive theory for Alzheimer's disease. Hypothesis:
Alzheimer's disease is caused by the cerebral accumulation and cytotoxicity of amyloid
β‐protein. Ann N Y Acad Sci. 2000;924(1):17-25.
[87] Hane F. Are amyloid fibrils molecular spandrels?. FEBS Lett. 2013;587(22):3617-3619.
[88] Murado MA, Vázquez JA, Rial D, et al. Dose–response modelling with two agents:
application to the bioassay of oil and shoreline cleaning agents. J Hazard Mater.
[89] Vázquez JA, Durán A, Rodríguez-Amado I, et al. Evaluation of toxic effects of several
carboxylic acids on bacterial growth by toxicodynamic modelling. Microb Cell Fact.
[90] Rial D, Vázquez JA, Murado MA. Effects of three heavy metals on the bacteria growth
kinetics: a bivariate model for toxicological assessment. Appl Microbiol Biotechnol.
Downloaded by [University of Florida] at 05:01 28 October 2017
[91] Vázquez JA. Modeling of chemical inhibition from amyloid protein aggregation kinetics.
BMC Pharmacol Toxicol. 2014;15(1):1.
[92] Vo T, Carulli D, Ehlert EM, et al. The chemorepulsive axon guidance protein
semaphorin3A is a constituent of perineuronal nets in the adult rodent brain. Mol Cell Neurosci.
[93] Wang Y, Xing J, Xu Y, et al. In silico ADME/T modelling for rational drug design. Q Rev
Biophys. 2015;48(04):488-515.
[94] Portelius E, Brinkmalm G, Tran A, et al. Identification of novel N-terminal fragments of
amyloid precursor protein in cerebrospinal fluid. Exp Neurol. 2010;223(2):351-358.
[95] Romero K, Ito K, Rogers JA, et al. The future is now: Model‐based clinical trial design for
Alzheimer's disease. Clin Pharmacol Ther. 2015;97(3):210-214.
[96] Fang H, Wang PF, Zhou Y, et al. Toll-like receptor 4 signaling in intracerebral hemorrhageinduced inflammation and injury. J Neuroinflammation. 2013;10(1):1.
[97] Mathew A, Fukuda T, Nagaoka Y, et al. Curcumin loaded-PLGA nanoparticles conjugated
with Tet-1 peptide for potential use in Alzheimer's disease. PLoS One. 2012;7(3):e32616.
[98] Cherry JD, Olschowka JA, O’Banion MK. Neuroinflammation and M2 microglia: the good,
the bad, and the inflamed. J Neuroinflammation. 2014;11(1):1.
[99] Michelucci A, Heurtaux T, Grandbarbe L, et al. Characterization of the microglial
phenotype under specific pro-inflammatory and anti-inflammatory conditions: effects of
oligomeric and fibrillar amyloid-β. J Neuroimmunol. 2009;210(1):3-12.
Downloaded by [University of Florida] at 05:01 28 October 2017
[100] Balce DR, Li B, Allan ER, et al. Alternative activation of macrophages by IL-4 enhances
the proteolytic capacity of their phagosomes through synergistic mechanisms. Blood.
[101] Liu S, Wang X, Li Y, et al. Necroptosis mediates TNF-induced toxicity of hippocampal
neurons. Biomed Res Int. 2014;2014.
[102] Vandenabeele P, Galluzzi L, Berghe TV, et al. Molecular mechanisms of necroptosis: an
ordered cellular explosion. Nat Rev Mol Cell Biol. 2010;11(10):700-714.
[103] Galluzzi L, Vanden Berghe T, Vanlangenakker N, et al. Programmed necrosis from
molecules to health and disease. Int Rev Cell Mol Biol. 2011;289:1-35.
[104] He S, Liang Y, Shao F, et al. Toll-like receptors activate programmed necrosis in
macrophages through a receptor-interacting kinase-3–mediated pathway. Proc Natl Acad Sci U S
A. 2011;108(50):20054-20059.
[105] Re DB, Le Verche V, Yu C, et al. Necroptosis drives motor neuron death in models of both
sporadic and familial ALS. Neuron. 2014;81(5):1001-1008.
[106] Parry TL, Melehani JH, Ranek MJ, et al. Functional amyloid signaling via the
inflammasome, necrosome, and signalosome: new therapeutic targets in heart failure. Front
Cardiovasc Med. 2015;2.
[107] Ather JL, Ckless K, Martin R, et al. Serum amyloid A activates the NLRP3 inflammasome
and promotes Th17 allergic asthma in mice. J Immunol. 2011;187(1):64-73.
Downloaded by [University of Florida] at 05:01 28 October 2017
[108] Hafner-Bratkovič I, Benčina M, Fitzgerald KA, et al. NLRP3 inflammasome activation in
macrophage cell lines by prion protein fibrils as the source of IL-1β and neuronal toxicity. Cell
Mol Life Sci. 2012;69(24):4215-4228.
[109] Munoz L, Ranaivo HR, Roy SM, et al. A novel p38α MAPK inhibitor suppresses brain
proinflammatory cytokine up-regulation and attenuates synaptic dysfunction and behavioral
deficits in an Alzheimer's disease mouse model. J Neuroinflammation. 2007;4(1):1.
[110] Evans CG, Wisén S, Gestwicki JE. Heat shock proteins 70 and 90 inhibit early stages of
amyloid β-(1–42) aggregation in vitro. J Biol Chem. 2006;281(44):33182-33191.
[111] Flower TR, Chesnokova LS, Froelich CA, et al. Heat shock prevents alpha-synucleininduced apoptosis in a yeast model of Parkinson's disease. J Mol Biol. 2005;351(5):1081-1100.
[112] Daturpalli S, Waudby CA, Meehan S, et al. Hsp90 inhibits α-synuclein aggregation by
interacting with soluble oligomers. J Mol Biol. 2013;425(22):4614-4628.
[113] Fernandez-Funez P, Casas-Tinto S, Zhang Y, et al. In vivo generation of neurotoxic prion
protein: role for hsp70 in accumulation of misfolded isoforms. PLoS Genet. 2009;5(6):e1000507.
[114] Sawiris GP, Becker KG, Elliott EJ, et al. Molecular analysis of bovine spongiform
encephalopathy infection by cDNA arrays. J Gen Virol. 2007;88(4):1356-1362.
[115] Kumar N, Gaur D, Gupta A, et al. Hsp90-associated immunophilin homolog Cpr7 is
required for the mitotic stability of [URE3] prion in Saccharomyces cerevisiae. PLoS Genet.
[116] Seo H, Sonntag KC, Kim W, et al. Proteasome activator enhances survival of Huntington's
disease neuronal model cells. PloS One. 2007;2(2):e238.
Downloaded by [University of Florida] at 05:01 28 October 2017
[117] Lee BH, Lee MJ, Park S, et al. Enhancement of proteasome activity by a small-molecule
inhibitor of USP14. Nature. 2010;467(7312):179-184.
[118] Svensson E, Horváth‐Puhó E, Thomsen RW, et al. Vagotomy and subsequent risk of
Parkinson's disease. Ann Neurol. 2015;78(4):522-529.
[119] Stokholm MG, Danielsen EH, Hamilton‐Dutoit SJ, et al. Pathological α‐synuclein in
gastrointestinal tissues from prodromal Parkinson disease patients. Ann Neurol. 2016;79(6):940949.
[120] Rees K, Stowe R, Patel S, et al. Helicobacter pylori eradication for Parkinson's disease.
Cochrane Libr. 2011.
[121] Shu Q, Crick SL, Pinkner JS, et al. The E. coli CsgB nucleator of curli assembles to βsheet oligomers that alter the CsgA fibrillization mechanism. Proc Natl Acad Sci U S A.
[122] Dueholm MS, Søndergaard MT, Nilsson M, et al. Expression of Fap amyloids in
Pseudomonas aeruginosa, P. fluorescens, and P. putida results in aggregation and increased
biofilm formation. Microbiologyopen. 2013;2(3):365-382.
[123] Marcoleta A, Marín M, Mercado G, et al. Microcin E492 amyloid formation is retarded by
posttranslational modification. J bacteriol. 2013;195(17):3995-4004.
[124] Ramsugit S, Pillay M. Pili of Mycobacterium tuberculosis: current knowledge and future
prospects. Arch Microbiol. 2015;197(6):737-744.
[125] Todorova TT, Tsankova GS, Ermenlieva NM. Yeast prion protein Ure2p – a useful model
Downloaded by [University of Florida] at 05:01 28 October 2017
for human prion diseases. Journal of IMAB. 2015;21(1): 747-751.
[126] Bengtson MH, Joazeiro CA. Role of a ribosome-associated E3 ubiquitin ligase in protein
quality control. Nature. 2010;467(7314):470-473.
[127] Ren Q, Kwan AH, Sunde M. Two forms and two faces, multiple states and multiple uses:
Properties and applications of the self‐assembling fungal hydrophobins. Peptide Science.
[128] Macindoe I, Kwan AH, Ren Q, et al. Self-assembly of functional, amphipathic amyloid
monolayers by the fungal hydrophobin EAS. Proc Natl Acad Sci U S A. 2012;109(14):E804E811.
[129] Pham CL, Kwan AH, Sunde M. Functional amyloid: widespread in Nature, diverse in
purpose. Essays Biochem. 2014;56:207-219.
[130] Rising A, Johansson J. Toward spinning artificial spider silk. Nat Chem Biol.
[131] Zhou Y, Blanco LP, Smith DR, et al. Amyloid Proteins: Methods and Protocols. 2nd ed.
New York (NY): Humana Press; 2012. Chapter 21, Bacterial Amyloids; p. 303-320. (Methods
in Molecular Biology; 849).
[132] Nishimori JH, Newman TN, Oppong GO, et al. Microbial amyloids induce interleukin 17A
(IL-17A) and IL-22 responses via Toll-like receptor 2 activation in the intestinal mucosa. Infect
Immun. 2012;80(12):4398-4408.
[133] Harry GJ. Microglia during development and aging. Pharmacol Ther. 2013;139(3):313326.
Downloaded by [University of Florida] at 05:01 28 October 2017
[134] Tükel Ç, Wilson RP, Nishimori JH, et al. Responses to amyloids of microbial and host
origin are mediated through toll-like receptor 2. Cell Host Microbe. 2009;6(1):45-53.
[135] Zhang J, Ke KF, Liu Z, et al. Th17 Cell-Mediated Neuroinflammation Is Involved in
Neurodegeneration of Aβ 1-42-Induced Alzheimer’s Disease Model Rats. PLoS One.
[136] Thackray AM, McKenzie AN, Klein MA, et al. Accelerated prion disease in the absence of
interleukin-10. J Virol. 2004;78(24):13697-13707.
[137] Hamilton JA, Whitty G, White AR, et al. Alzheimer’s disease amyloid beta and prion
protein amyloidogenic peptides promote macrophage survival, DNA synthesis and enhanced
proliferative response to CSF-1 (M-CSF). Brain Res. 2002;940(1):49-54.
[138] Nordstedt C, Näslund J, Tjernberg LO, et al. The Alzheimer A beta peptide develops
protease resistance in association with its polymerization into fibrils. J Biol Chem.
[139] Sitaras C, Naghavi M, Herrington MB. Sodium dodecyl sulfate–agarose gel
electrophoresis for the detection and isolation of amyloid curli fibers. Anal Biochem.
[140] Jendroska K, Heinzel FP, Torchia M, et al. Proteinase‐resistant prion protein accumulation
in Syrian hamster brain correlates with regional pathology and scrapie infectivity. Neurology.
[141] Buxbaum JN, Linke RP. A molecular history of the amyloidoses. J Mol Biol.
Downloaded by [University of Florida] at 05:01 28 October 2017
[142] Sabate R, Rodriguez-Santiago L, Sodupe M, et al. Thioflavin-T excimer formation upon
interaction with amyloid fibers. Chem Commun. 2013;49(51):5745-5747.
Alzheimer’s disease (AD); Amyloid beta 1-42 (Aβ 1-42/ Aβ42); Amyloid precursor protein
(APP); Amyotrophic lateral sclerosis (ALS); Bovine Spongiform Encephalopathies (BSE);
Central nervous system (CNS); Creutzfeldt Jacob Disease (CJD); Follecular Dendritic Cells
(FDC); Functional bacterial amyloid (FuBA); Gastrointestinal (GI); Interlukin (IL); Lipo poly
saccharide (LPS); Mixed lineage kinase domain like protein (MLKL); Multiple System atrophy
(MSA); Parkinson’s Disease (PD); Pathogen associated molecular pattern (PAMP); Prion
Forming Domain (PFD); Prion Protein- Cellular (PrPC); Prion Protein- Scrapie (PrPSc); Receptor
interacting kinase 1 (RIP1); Receptor interacting kinase 3 (RIP3); RIP homotypic interaction
motif (RHIM); Shy-Drager syndrome (SDS); Thioflavin T (ThT); Toll like receptor (TLR);
Triggering receptor expressed in myeloid/microglial cells-2 (TREM2).
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Figure 1: A: Biogenesis of Curli fibers. Curli protein components- CsgG, F, E & D are
synthesized from one operon and CsgB, A & C from another. SecYEG (Sec tagged Curli
protein) secretes in periplasm and help making passage for Csg components. CsgC, E & G
altogether form a pore through which CsgF, B and soluble CsgA pass and come outside where
CsgB function as a nucleus to fibrillize CsgA monomers. CsgD acts as a regulator for
transcription of csgBAC operon. B: Biogenesis of fibrillar coating outside the arial hyphae of
Streptomyces coelicolor by Chaplin proteins. ChpA – ChpH diffuse out of the cell and form
insoluble layer of 4-6 nm wide fibrils between air and soil interface. This rigid film helps the
arial hyphae penetrating the soil barrier by lowering the water surface-tension. The change in
hydrophobicity in the reproductive aerial hyphae prevents it from growing back into the aqueous
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substrate and thus facilitates the dispersion of spores in wind.
Figure 2: Schematic representation showing clearance of Aβ42 monomer through
recognition by TREM2, Aβ fibril via TLR2 and functional bacterial amyloid (FuBA) via
TLR2. In brain, Aβ monomers are produced from Amyloid-β precursor protein (APP) through a
sequential cleavage by β and γ secretase enzymes. Mutations in presenilins (a component of γ
secretase) increase the production of Aβ42 which lead to the Amyloid β oligomerization, fibril
formation and ultimately senile plaque formation. Triggering receptor expressed in
myeloid/microglial cells-2 (TREM2) in association with the membrane-spanning linker protein
TYROBP clear these amyloid β monomers through phagocytosis and Toll Like Receptors-2
(TLR2) clear the fibrils. The ROS generated via TLR2 signaling pathway down-regulate TREM2
and thus Aβ42 monomer clearance via TREM2 is inhibited. There is still some lack of evidence
that FuBA (functional beta amyloids) cross the Blood Brain Barrier (BBB) but there is evidence
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that, FuBA also down-regulate TREM2 expression via ROS generation. Thus in this scenario,
the lack of clearance of amyloid beta monomers increases the rate of senile plaque formation.
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Figure 3: Schematic representation showing infectious prion protein- PrPSc replication
hypothesis. According to this hypothesis, a pathogenic PrPSc molecule exists in a fibrillar form,
which when transmitted into a healthy individual, binds normal, cellular prion- PrPC molecules.
With the subsequent conformational change of PrPC molecule to that of PrPSc, the PrPSc-fibril
elongates. In the following steps, more and more cellular prions (PrPC) are converted to PrPSc
form through the conformational change induced by infection seed i.e. the first infectious PrPSc
fibril and are added up to the growing PrPSc chain, resulting in the linear increase of PrPSc-fibril.
The exponential growth of pathogenic PrPSc molecules takes place with the aid of a reverse
breakage step, generating multiple new PrPSc seeds from elongated PrPSc-fibril. This facilitates
amyloid plaque formation through the aggregation of the newly synthesized PrP Sc-fibrils.
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Table 1: β-Amyloids are diverse among organisms with varying functions
Amyl Primary Amino Acid Sequencea (Related)
- E. coli,
Salmonel A)
la spp.
and CD.
yces sp.
of water
and EM.
tension (i.e.
nt of aerial
Pseudom FapC
Not reported
forms pores
pneumon E492
cytoplasmic CD,
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on pili.
red and
Not reported
(Upto 50th AA-out of total 350
of nitrogen
on, X-
red, EM
(Upto 50th AA-of 680 residues.)
of stop-
codon read-
red, CD
and X-
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(Upto 50th AA out of 110 residues)
Fungal coat
of adhesion
and surface
red and
(Upto 50th out of 110 AA residues of D.
red, X-
and fish
functions in
and CD.
EM and
Not reported
(i.e. spider
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Upto 50th out of 660 residues-
red, EM
n of toxic
es during
EM, Electron Microscopy; CD, Circular Dichroism Spectroscopy; ThioT, Thioflavin-T test; TEM,
Transmission Electron Microscopy; FTIR, Fourier Transform Infra Red spectroscopy; MS, Mass
Spectroscopy; MALDI-TOF, Matrix Assisted Laser Desorption Ionization-Time of Flight; NMR,
Nuclear Magnetic Resonance; AFM, Atomic Force Microscopy;
mentioned in one letter amino acid code.
Table 2: The overall comparison between Aβ42- Prions- Functional amyloids
Names of different amyloids
Disease assotiated amyloids
Functional amyloids
Covering a huge range
Aβ42 of Alzheimer’s
Human being
Mammals, mainly
sheep, cows and
 Filamentous,
 Mammalian
cellular prion
sheet structures with
beta-sheet that
PrPC is a α-
indefinite length and
yields twisted fibers
a diameter of about
of about 10 nm
2-20 nm.
diameters & the
protein but
senile plaques of
misfolded PrPSc
AD are made up of
is a β-amyloid
long, unbranched 4-
10 nanometer wide
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from E. coli to Homo
 Most
frequently  Stacking subunits
employs the stacking
may not be stably
of folded subunits.
 Possess
 Possess parallel in-  Structural
or anti-parallel βare
(Ure2, Sup35, Rnq1,
of parallel & anti-
parallel β-sheets.
sheet structure.
(HET-s, CsgA) and
from Aβ42
by PrPSc
biofilm formation/ host accumulating as senile amyloid plaques and
invasion/ development of plaques
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cause causes
structures/ neurodegeneration in encephalopathy,
formation/ AD.
particularly BSE in
Adhesive properties on
pili/ working as toxins/
sheep & CJD in
formation/Regulation of
nitrogen catabolism & so
Misfolded proteins
and/or Mode monomers secret outside
after synthesis start
of action
& assemble together;
chain elongation; e.g.,
e.g., CsgA secretes
Aβ42 monomers
cellular prions; e.g.,
outside the cells→ CsgB
aggregation→ Aβ42
entry of infectious
nucleates fibrillization of
PrPSc fibril in host→
CsgA→CsgG acts as
Aggregation of
outer membrane pore→
For structural FuBA-
secretes CsgA and CsgB. plaque formation.
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exponential increase
Role in
FuBA functions as a
Aβ is considered to be Contagious
toxin & may cause
the causative agent of fibril
disease in host e.g. MTP
disease (AD) onset.
of M. tuberculosis.
plaque deposition.
CsgA contains the
Aβ42 acting as a
After entry via M-
(PAMP) that is
PAMP [133], is
cells, encountered by
recognized by TLR2
recognized by TLR2
[131] & induce IL-17A,
on microglia [134],
replicates in FDC→
drives NF-kB signaling
which leads to
and cyclooxygenase-2
neuropathology via
activation [132].
inflammation [135].
IL4, IL10, IL13→
Having a common beta strand rich structure all the above amyloids
appear as an insoluble biomolecule and treatment with formic acid or
hexa-fluoro-2-propanol is required to liberate monomers from these fibers
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FuBAs or disease assotiated amyloids like Aβ42 or prion proteins (PrPSc)
are highly resistance to protease digestion [138-140].
Congo red which stains the beta-pleated sheet structures can stain both
detection &
these pathogenic Aβ42 and bacterial amyloids [141]. Congo red staining
results in a red shift in spectro-photometer analysis and green
birefringence under polarized light [36]. Amyloids belonging to any
category, gives a positive thioflavin T test (ThT) resulting in increased
fluorescence [142].
Different types of amyloids are beyond evolutionary selection constrain.
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Table 3: Symbolic notations used for the mathematical equation and corresponding units
ThT fluorescence intensity at 460 nm to 520 nm. Units: absorbance units
(AU) or (%).
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Time. Units: h or d.
Maximum aggregation growth. Units: AU or %
Maximum aggregation rate. Units: AU/h, AU d−1 or % h-1

Lag phase. Units: h or d.
Maximum aggregation affected by functional amyloid. Units: AU or %
Maximum aggregation rate affected by functional amyloid. Units: AU/h,
AU d-1 or % h-1
Lag phase affected by functional amyloid. Units: h or d
Concentration of functional amyloid. Units: mM or μM.
Maximum response affecting on Xm Dimensionless
Concentration corresponding to the semi-maximum response affecting
on Xm Units: mM or μM
Shape parameter affecting on Xm Dimensionless
Maximum response affecting on vm Dimensionless
Concentration corresponding to the semi-maximum response affecting
on vm Units: mM or μM
Shape parameter affecting on vm Dimensionless
Maximum response affecting on  Dimensionless
Concentration corresponding to the semi-maximum response affecting on
 Units: mM or μM
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Shape parameter affecting on  Dimensionless
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