Bacterial Amyloid Research Articles

The Roles of Functional Bacterial Amyloids in Neurological Physiology and Pathophysiology: Pros and Cons for Neurodegeneration.

Bacterial biofilms, which are complex communities of microorganisms encapsulated in a self-produced extracellular matrix, play critical roles in various diseases. Recent research has underscored the dualistic nature of amyloids, structural proteins within these biofilms, in human health, particularly highlighting the significant role in neurodegenerative disorders such as Alzheimer's (AD) and Parkinson's disease (PD). These amyloids modulate the immune response by inducing the production of interleukin-10 (IL-10), which plays a role in anti-inflammatory processes. Additionally, they inhibit the aggregation of human amyloids and enhance the integrity of the intestinal barrier. Detrimentally, they exacerbate neuroinflammation by elevating inflammatory cytokines and promoting the aggregation of human amyloid proteins-amyloid-β (Aβ) in AD and α-synuclein (αS) in PD-through a process known as cross-seeding. Moreover, bacterial amyloids have also been shown to stimulate the production of anti-curli/DNA antibodies, which are implicated in the pathogenesis of autoimmune diseases. Given their dualistic nature, bacterial amyloids may, under specific conditions, function as beneficial proteins for human health. This understanding holds promise for the development of targeted therapeutic strategies aimed at modulating bacterial amyloids in the context of neurodegenerative diseases, such as AD and PD.

Computational exploration of the self-aggregation mechanisms of phenol-soluble modulins β1 and β2 in Staphylococcus aureus biofilms.

The formation of functional bacterial amyloids by phenol-soluble modulins (PSMs) in Staphylococcus aureus is a critical component of biofilm-associated infections, providing robust protective barriers against antimicrobial agents and immune defenses. Clarifying the molecular mechanisms of PSM self-assembly within the biofilm matrix is essential for developing strategies to disrupt biofilm integrity and combat biofilm-related infections. In this study, we analyzed the self-assembly dynamics of PSM-β1 and PSM-β2 by examining their folding and dimerization through long-timescale atomistic discrete molecular dynamics simulations. Our findings revealed that both peptides primarily adopt helical structures as monomers but shift to β-sheets upon dimerization. Monomeric state, PSM-β1 exhibited frequent transitions between helical and β-sheet forms, while PSM-β2 largely retained a helical structure. Upon dimerization, both peptides showed pronounced β-sheet formation around conserved C-terminal residues 21-44. Residues 21-33, largely unstructured as monomers, demonstrated strong tendencies for β-sheet formation and intermolecular interactions, underscoring their central role in the self-assembly of both peptides. Additionally, the PSM-β1 N-terminus formed β-sheets only when interacting with the C-terminus, whereas the PSM-β2 N-terminus remained helical and uninvolved in β-sheet formation. These distinct aggregation behaviors likely contribute to biofilm dynamics, with C-terminal regions facilitating biofilm formation and N-terminal regions influencing stability. Targeting residues 21-33 in PSM-β1 and PSM-β2 offers a promising therapeutic approach for disrupting biofilm integrity. This study advances our understanding of PSM-β1 and PSM-β2 self-assembly and presents new targets for drug design against biofilm-associated diseases.

Surpassing protein specificity in biomimetics of bacterial amyloids.

In nature, nontoxic protein amyloids serve as dynamic, protein-specific depots, exemplified by both bacterial inclusion bodies and secretory granules from the endocrine system. Inspired by these systems, chemically defined and regulatory-compliant artificial protein microgranules have been developed for clinical applications as endocrine-like protein repositories. This has been achieved by exploiting the reversible coordination between histidine residues and divalent cations such as Zn+2, that promotes protein-protein interactions. While stereospecificity is a main architectonic feature of natural amyloids, the potential for synthetic approaches to create hybrid protein materials remains unexplored. Such materials could enable the occurrence and synchronized local application of diverse proteins in predefined molar ratios, for coupled enzymatic reactions or delivery of synergistically acting polypeptides. Here, we report on the fabrication of artificial protein granules with amyloidal architecture formed by combining two structurally distinct polypeptides. Specifically, we tested co-aggregation of the pairs GFP/IRFP and GFP/β-galactosidase. The formation of hybrid microparticles was confirmed through FRET and complementary methodologies, demonstrating that the His-Zn clustering technology does not require sequential or structural homologies between aggregating polypeptides. This approach opens new avenues for the development of functional depots that capitalize on synergistic protein functionalities, paving the way for next-generation functional materials.

Pathogenesis-Associated Bacterial Amyloids: The Network of Interactions.

Amyloids are protein fibrils with a characteristic cross-β structure that is responsible for the unusual resistance of amyloids to various physical and chemical factors, as well as numerous pathogenic and functional consequences of amyloidogenesis. The greatest diversity of functional amyloids was identified inbacteria. The majority of bacterial amyloids are involved in virulence and pathogenesis either via facilitating formation of biofilms and adaptation of bacteria to colonization of a host organism or through direct regulation of toxicity. Recent studies have shown that, beside their commonly known activity, amyloids may be involved in the spatial regulation of proteome by modulating aggregation of other amyloidogenic proteins with multiple functional or pathological effects. Although the studies on the role of microbiome-produced amyloids in the development of amyloidoses in humans and animals have only been started, it is clear that humans as holobionts contain amyloids encoded not only by the host genome, but also by microorganisms that constitute the microbiome. Amyloids acquired from external sources (e.g., food) can interact with holobiont amyloids and modulate the effects of bacterial and host amyloids, thus adding another level of complexity to the holobiont-associated amyloid network. In this review, we described bacterial amyloids directly or indirectly involved in disease pathogenesis in humans and discussed the significance of bacterial amyloids inthe three-component network of holobiont-associated amyloids.

Young rat microbiota extracts strongly inhibit fibrillation of α-synuclein and protect neuroblastoma cells and zebrafish against α-synuclein toxicity

The clinical manifestations of Parkinson's Disease (PD) are driven by aggregation of α-Synuclein (α-Syn) in the brain. However, there is increasing evidence that PD may be initiated in the gut and thence spread to the brain, e.g. via the vagus nerve. Many studies link PD to changes in the gut microbiome, and bacterial amyloid has been shown to stimulate α-syn aggregation. Yet we are not aware of any studies reporting on a direct connection between microbiome components and α-Syn aggregation. Here we report that soluble extract from the gut microbiome of the rats, particularly young rats transgenic for PD, show a remarkably strong ability to inhibit in vitro α-Syn aggregation and keep it natively unfolded and monomeric. The active component(s) are heat-labile molecule(s) of around 30-100 kDa size which are neither nucleic acid nor lipid. Proteomic analysis identified several proteins whose concentrations in different rat samples correlated with the samples’ anti-inhibitory activity, while a subsequent pulldown assay linked the protein chaperone DnaK with the inhibitory activity of young rat’s microbiome, confirmed in subsequent in vitro assays. Remarkably, the microbiome extracts also protected neuroblastoma SH-SY5Y cells and zebrafish embryos against α-Syn toxicity. Our study sheds new light on the gut microbiome as a potential source of protection against PD and opens up for new microbiome-based therapeutic strategies.

Role of the Gut Microbiome and Bacterial Amyloids in the Development of Synucleinopathies (Review)

Role of the Gut Microbiome and Bacterial Amyloids in the Development of Synucleinopathies (Review)

Bacterial amyloid curli activates the host unfolded protein response via IRE1α in the presence of HLA-B27

ABSTRACT Salmonella enterica serovar Typhimurium (STm) causes gastroenteritis and can progress to reactive arthritis (ReA). STm forms biofilms in the gut that secrete the amyloid curli, which we previously demonstrated can trigger autoimmunity in mice. HLA-B27 is a genetic risk factor for ReA; activation of the unfolded protein response (UPR) due to HLA-B27 misfolding is thought to play a critical role in ReA pathogenesis. To determine whether curli exacerbates HLA-B27-induced UPR, bone marrow-derived macrophages (BMDMs) isolated from HLA-B27 transgenic (tg) mice were used. BMDMs treated with purified curli exhibited elevated UPR compared to C57BL/6, and curli-induced IL-6 was reduced by pre-treating macrophages with inhibitors of the IRE1α branch of the UPR. In BMDMs, intracellular curli colocalized with GRP78, a regulator of the UPR. In vivo, acute infection with wild-type STm increased UPR markers in the ceca of HLA-B27tg mice compared to C57BL/6. STm biofilms that contain curli were visible in the lumen of cecal tissue sections. Furthermore, curli was associated with macrophages in the lamina propria, colocalizing with GRP78. Together, these results suggest that UPR plays a role in the curli-induced inflammatory response, especially in the presence of HLA-B27, a possible mechanistic link between STm infection and genetic susceptibility to ReA.

Amyloid, Crohn's disease, and Alzheimer's disease - are they linked?

Crohn's disease (CD) is a chronic inflammatory disease that most frequently affects part of the distal ileum, but it may affect any part of the gastrointestinal tract. CD may also be related to systemic inflammation and extraintestinal manifestations. Alzheimer's disease (AD) is the most common neurodegenerative disease, gradually worsening behavioral and cognitive functions. Despite the meaningful progress, both diseases are still incurable and have a not fully explained, heterogeneous pathomechanism that includes immunological, microbiological, genetic, and environmental factors. Recently, emerging evidence indicates that chronic inflammatory condition corresponds to an increased risk of neurodegenerative diseases, and intestinal inflammation, including CD, increases the risk of AD. Even though it is now known that CD increases the risk of AD, the exact pathways connecting these two seemingly unrelated diseases remain still unclear. One of the key postulates is the gut-brain axis. There is increasing evidence that the gut microbiota with its proteins, DNA, and metabolites influence several processes related to the etiology of AD, including β-amyloid abnormality, Tau phosphorylation, and neuroinflammation. Considering the role of microbiota in both CD and AD pathology, in this review, we want to shed light on bacterial amyloids and their potential to influence cerebral amyloid aggregation and neuroinflammation and provide an overview of the current literature on amyloids as a potential linker between AD and CD.

Characterizing inflammasome activation by bacterial amyloid curli complexes from biofilms in dendritic cells and its role in SLE

Abstract Bacterial infections are a crucial environmental trigger for flares in Systemic lupus erythematosus (SLE). Although these infections are common in lupus patients, a precise mechanism of action remains unknown. Bacteria protect themselves from stresses by embedding in an extracellular matrix to form biofilms. Biofilms from bacterial species such as E. coli and Salmonella contain an amyloid protein called curli. Previous work from our labs has shown that curli/DNA complexes can accelerate lupus-like disease in mice, and increased levels of anti-curli antibodies are associated with flares in SLE patients, making these complexes important in autoimmunity. We had previously found that curli/DNA is a potent trigger of immune activation in dendritic cells (DCs) and macrophages. In macrophages, curli/DNA was also reported to induce IL-1b production through activation of the NLRP3 inflammasome. Here we expand these studies to delineate how curli/DNA complexes regulate IL-1b in murine and human DCs. Using curli/DNA alone or in combination with inflammasome stimuli, we found that curli/DNA stimulate pro-IL1b expression and inflammasome assembly, leading to caspase 1 activation, cleavage and release of mature IL-1B by DCs. However, we observed no cell death post inflammasome activation, suggesting a hyperactivated state in stimulated DCs. A deeper knowledge of this molecular mechanism might shed light on the role of inflammasome activation by bacterial infections in escalating SLE.

De la microbiota como “cisne negro”: El extraño caso de los amiloides bacterianos y la neurodegeneración

The human microbiota is the complex community of microorganisms that colonize our epithelia, with a special presence in the large intestine. Recent research links the microbiota to various pathologies, among which I will focus here on neurodegenerative diseases. Metabolites generated by the bacteria of our microbiota have inflammation-modulating properties, interacting with specific receptors in the intestinal epithelium, permeating the underlying tissue and making their way into the blood vessels, thus reaching the central nervous system (CNS). On the other hand, proteins with the potential to aggregate in the form of amyloids, secreted by bacteria to build the matrix that interweaves the biofilms that allow them to persist in the intestine, can use an alternative route to reach the CNS: the parasympathetic endings of the vagus nerve, spreading as prions (infective amyloids), in what is known as the “gut-brain axis”. Once in the CNS, bacterial amyloids can promote aggregation of amyloidogenic proteins involved in neurodegeneration (α-synuclein, Tau, Ab, Sod1). This article reviews and discusses some of the recent experimental evidence that, mainly in animal model systems, assigns a central role for the microbiota in the aetiology of neurodegenerative diseases, as well as the studies performed in the laboratory of the author that have led to the development of a minimal, exclusively bacterial model system that recapitulates essential molecular aspects of a neurodegenerative disease. Keywords: microbiota; neurodegeneration; microbial metabolites; bacterial amyloids; prions; RepA-WH1

Role of the Gut Microbiome and Bacterial Amyloids in the Development of Synucleinopathies.

Less than ten years ago, evidence began to accumulate about association between the changes in the composition of gut microbiota and development of human synucleinopathies, in particular sporadic form of Parkinson's disease. We collected data from more than one hundred and thirty experimental studies that reported similar results and summarized the frequencies of detection of different groups of bacteria in these studies. It is important to note that it is extremely rare that a unidirectional change in the population of one or another group of microorganisms (only an elevation or only a reduction) was detected in the patients with Parkinson's disease. However, we were able to identify several groups of bacteria that were overrepresented in the patients with Parkinson's disease in the analyzed studies. There are various hypotheses about the molecular mechanisms that explain such relationships. Usually, α-synuclein aggregation is associated with the development of inflammatory processes that occur in response to the changes in the microbiome. However, experimental evidence is accumulating on the influence of bacterial proteins, including amyloids (curli), as well as various metabolites, on the α-synuclein aggregation. In the review, we provided up-to-date information about such examples.

Intrinsically disordered Pseudomonas chaperone FapA slows down the fibrillation of major biofilm-forming functional amyloid FapC.

Functional bacterial amyloids play a crucial role in the formation of biofilms, which mediate chronic infections and contribute to antimicrobial resistance. This study focuses on the FapC amyloid fibrillar protein from Pseudomonas, a major contributor to biofilm formation. We investigate the initial steps of FapC amyloid formation and the impact of the chaperone-like protein FapA on this process. Using solution nuclear magnetic resonance (NMR), we recently showed that both FapC and FapA are intrinsically disordered proteins (IDPs). Here, the secondary structure propensities (SSPs) are compared to alphafold (DeepMind, protein structure prediction tool/algorithm: https://alphafold.ebi.ac.uk/) models. We further demonstrate that the FapA chaperone interacts with FapC and significantly slows down the formation of FapC fibrils. Our NMR titrations reveal ~ 18% of the resonances show FapA-induced chemical shift perturbations (CSPs), which has not been previously observed, the largest being for A82, N201, C237, C240, A241, and G245. These sites may suggest a specific interaction site and/or hotspots of fibrillation inhibition/control interface at the repeat-1 (R1)/loop-2 (L2) and L2/R3 transition areas and at the C-terminus of FapC. Remarkably, ~ 90% of FapA NMR signals exhibit substantial CSPs upon titration with FapC, the largest being for S63, A69, A80, and I92. A temperature-dependent effect of FapA was observed on FapC by thioflavin T (ThT) and NMR experiments. This study provides a detailed understanding of the interaction between the FapA and FapC, shedding light on the regulation and slowing down of amyloid formation, and has important implications for the development of therapeutic strategies targeting biofilms and associated infections.

The Amyloid Assembly of the Bacterial Hfq Is Lipid-Driven and Lipid-Specific.

Under specific conditions, some proteins can self-assemble into fibrillar structures called amyloids. Initially, these proteins were associated with neurodegenerative diseases in eucaryotes. Nevertheless, they have now been identified in the three domains of life. In bacteria, they are involved in diverse biological processes and are usually useful for the cell. For this reason, they are classified as "functional amyloids". In this work, we focus our analysis on a bacterial functional amyloid called Hfq. Hfq is a pleiotropic regulator that mediates several aspects of genetic expression, mainly via the use of small noncoding RNAs. Our previous work showed that Hfq amyloid-fibrils interact with membranes. This interaction influences Hfq amyloid structure formation and stability, but the specifics of the lipid on the dynamics of this process is unknown. Here, we show, using spectroscopic methods, how lipids specifically drive and modulate Hfq amyloid assembly or, conversely, its disassembly. The reported effects are discussed in light of the consequences for bacterial cell life.

Serum Amyloid A3 Fuels a Feed-Forward Inflammatory Response to the Bacterial Amyloid Curli in the Enteric Nervous System

BackgroundMounting evidence suggests a role for the gastro-intestinal microbiome as a determinant of peripheral immunity and central neurodegeneration, but the local disease mechanisms remain unknown. Given its potential relevance for early diagnosis and therapeutic intervention, we set out to map the pathogenic changes induced by bacterial amyloids in the gastro-intestinal tract and its enteric nervous system. MethodsTo examine the early response, we challenged primary murine myenteric networks with curli, the prototypic bacterial amyloid, and performed shotgun RNA sequencing and multiplex ELISA. Using enteric neurosphere-derived glial and neuronal cell cultures, as well as in vivo curli injections into the colon wall, we further scrutinized curli-induced pathogenic pathways. ResultsCurli induced a pro-inflammatory response, with marked upregulation of Serum Amyloid A3 (Saa3) and the secretion of several cytokines. This pro-inflammatory state was primarily induced in enteric glia, was accompanied by elevated levels of DNA damage and replication, and triggered the influx of immune cells in vivo. The addition of recombinant SAA3 was sufficient to recapitulate this specific pro-inflammatory phenotype while Saa3 knock-out attenuated curli-induced DNA damage and replication. Like curli, recombinant SAA3 caused a strong upregulation of Saa3 transcripts, indicating a feed-forward loop. Colonization of curli-producing Salmonella and Dextran Sulphate Sodium (DSS)-induced colitis caused a significant increase in Saa3 transcripts, indicating a central role for SAA3 in enteric dysfunction. Inhibition of dual leucine zipper kinase (DLK), an upstream regulator of the c-Jun N-terminal kinase (JNK) pathway responsible for SAA3 production, attenuated curli- and SAA3-induced Saa3 upregulation, DNA damage and replication in enteric glia. ConclusionsOur results position SAA3 as an important mediator of gastro-intestinal vulnerability towards bacterial-derived amyloids and demonstrate the potential of DLK inhibition to dampen enteric pathology.

Staphylococcus aureus functional amyloids catalyze degradation of β-lactam antibiotics

Antibiotic resistance of bacteria is considered one of the most alarming developments in modern medicine. While varied pathways for bacteria acquiring antibiotic resistance have been identified, there still are open questions concerning the mechanisms underlying resistance. Here, we show that alpha phenol-soluble modulins (PSMαs), functional bacterial amyloids secreted by Staphylococcus aureus, catalyze hydrolysis of β-lactams, a prominent class of antibiotic compounds. Specifically, we show that PSMα2 and, particularly, PSMα3 catalyze hydrolysis of the amide-like bond of the four membered β-lactam ring of nitrocefin, an antibiotic β-lactam surrogate. Examination of the catalytic activities of several PSMα3 variants allowed mapping of the active sites on the amyloid fibrils’ surface, specifically underscoring the key roles of the cross-α fibril organization, and the combined electrostatic and nucleophilic functions of the lysine arrays. Molecular dynamics simulations further illuminate the structural features of β-lactam association upon the fibril surface. Complementary experimental data underscore the generality of the functional amyloid-mediated catalytic phenomenon, demonstrating hydrolysis of clinically employed β-lactams by PSMα3 fibrils, and illustrating antibiotic degradation in actual S. aureus biofilms and live bacteria environments. Overall, this study unveils functional amyloids as catalytic agents inducing degradation of β-lactam antibiotics, underlying possible antibiotic resistance mechanisms associated with bacterial biofilms.

The Green Tea Polyphenol Epigallocatechin-Gallate (EGCG) Interferes with Microcin E492 Amyloid Formation

Microcin E492 (MccE492) is an antimicrobial peptide and proposed virulence factor produced by some Klebsiella pneumoniae strains, which, under certain conditions, form amyloid fibers, leading to the loss of its antibacterial activity. Although this protein has been characterized as a model functional amyloid, the secondary structure transitions behind its formation, and the possible effect of molecules that inhibit this process, have not been investigated. In this study, we examined the ability of the green tea flavonoid epigallocatechin gallate (EGCG) to interfere with MccE492 amyloid formation. Aggregation kinetics followed by thioflavin T binding were used to monitor amyloid formation in the presence or absence of EGCG. Additionally, synchrotron radiation circular dichroism (SRCD) and transmission electron microscopy (TEM) were used to study the secondary structure, thermal stability, and morphology of microcin E492 fibers. Our results showed that EGCG significantly inhibited the formation of the MccE492 amyloid, resulting in mainly amorphous aggregates and small oligomers. However, these aggregates retained part of the β-sheet SRCD signal and a high resistance to heat denaturation, suggesting that the aggregation process is sequestered or deviated at some stage but not completely prevented. Thus, EGCG is an interesting inhibitor of the amyloid formation of MccE492 and other bacterial amyloids.

OmpC and OmpF Outer Membrane Proteins of Escherichia coli and Salmonella enterica Form Bona Fide Amyloids.

Outer membrane proteins (Omps) of Gram-negative bacteria represent porins involved in a wide range of virulence- and pathogenesis-related cellular processes, including transport, adhesion, penetration, and the colonization of host tissues. Most outer membrane porins share a specific spatial structure called the β-barrel that provides their structural integrity within the membrane lipid bilayer. Recent data suggest that outer membrane proteins from several bacterial species are able to adopt the amyloid state alternative to their β-barrel structure. Amyloids are protein fibrils with a specific spatial structure called the cross-β that gives them an unusual resistance to different physicochemical influences. Various bacterial amyloids are known to be involved in host-pathogen and host-symbiont interactions and contribute to colonization of host tissues. Such an ability of outer membrane porins to adopt amyloid state might represent an important mechanism of bacterial virulence. In this work, we investigated the amyloid properties of the OmpC and OmpF porins from two species belonging to Enterobacteriaceae family, Escherichia coli, and Salmonella enterica. We demonstrated that OmpC and OmpF of E. coli and S. enterica form toxic fibrillar aggregates in vitro. These aggregates exhibit birefringence upon binding Congo Red dye and show characteristic reflections under X-ray diffraction. Thus, we confirmed amyloid properties for OmpC of E. coli and demonstrated bona fide amyloid properties for three novel proteins: OmpC of S. enterica and OmpF of E. coli and S. enterica in vitro. All four studied porins were shown to form amyloid fibrils at the surface of E. coli cells in the curli-dependent amyloid generator system. Moreover, we found that overexpression of recombinant OmpC and OmpF in the E. coli BL21 strain leads to the formation of detergent- and protease-resistant amyloid-like aggregates and enhances the birefringence of bacterial cultures stained with Congo Red. We also detected detergent- and protease-resistant aggregates comprising OmpC and OmpF in S. enterica culture. These data are important in the context of understanding the structural dualism of Omps and its relation to pathogenesis.

Bionanocomposites with Enhanced Physical Properties from Curli Amyloid Assemblies and Cellulose Nanofibrils.

Proteinaceous amyloid fibrils are one of the stiffest biopolymers due to their extensive cross-β-sheet quaternary structure, whereas cellulose nanofibrils (CNFs) exhibit interesting properties associated with their nanoscale size, morphology, large surface area, and biodegradability. Herein, CNFs were supplemented with amyloid fibrils assembled from the Curli-specific gene A (CsgA) protein, the main component of bacterial biofilms. The resulting composites showed superior mechanical properties, up to a 7-fold increase compared to unmodified CNF films. Wettability and thermogravimetric analyses demonstrated high surface hydrophobicity and robust thermal tolerance. Bulk spectroscopic characterization of CNF-CsgA films revealed key insights into the molecular organization within the bionanocomposites. Atomic force microscopy and photoinduced force microscopy revealed the high-resolution location of curli assemblies into the CNF films. This novel sustainable and cost-effective CNF-based bionanocomposites supplemented with intertwined bacterial amyloid fibrils opens novel directions for environmentally friendly applications demanding high mechanical, water-repelling properties, and thermal resistance.

Solution-state NMR assignment and secondary structure analysis of the monomeric Pseudomonas biofilm-forming functional amyloid accessory protein FapA.

FapA is an accessory protein within the biofilm forming functional bacterial amyloid related fap-operon in Pseudomonas, and maybe a chaperone for FapC controlling its fibrillization. To allow further structural analysis, here we present a complete sequential assignment of 1Hamide, 13Cα, 13Cβ, and 15N NMR resonances for the functional form of the monomeric soluble FapA protein, comprising amino acids between 29 and 152. From these observed chemical shifts, the secondary structure propensities (SSPs) were determined. FapA predominantly adopts a random coil conformation, however, we also identified small propensities for α-helical and β-strand conformations. Notably, these observed SSPs are smaller compared to the ones we recently observed for the monomeric soluble FapC protein. These NMR results provide valuable insights into the activity of FapA in functional amyloid formation and regulation, that will also aid developing strategies targeting amyloid formation within biofilms and addressing chronic infections.

Effect of Bacterial Amyloid Protein Phenol-Soluble Modulin Alpha 3 on the Aggregation of Amyloid Beta Protein Associated with Alzheimer's Disease.

Since the proposal of the brainstem axis theory, increasing research attention has been paid to the interactions between bacterial amyloids produced by intestinal flora and the amyloid β-protein (Aβ) related to Alzheimer's disease (AD), and it has been considered as the possible cause of AD. Therefore, phenol-soluble modulin (PSM) α3, the most virulent protein secreted by Staphylococcus aureus, has attracted much attention. In this work, the effect of PSMα3 with a unique cross-α fibril architecture on the aggregation of pathogenic Aβ40 of AD was studied by extensive biophysical characterizations. The results proposed that the PSMα3 monomer inhibited the aggregation of Aβ40 in a concentration-dependent manner and changed the aggregation pathway to form granular aggregates. However, PSMα3 oligomers promoted the generation of the β-sheet structure, thus shortening the lag phase of Aβ40 aggregation. Moreover, the higher the cross-α content of PSMα3, the stronger the effect of the promotion, indicating that the cross-α structure of PSMα3 plays a crucial role in the aggregation of Aβ40. Further molecular dynamics (MD) simulations have shown that the Met1-Gly20 region in the PSMα3 monomer can be combined with the Asp1-Ala2 and His13-Val36 regions in the Aβ40 monomer by hydrophobic and electrostatic interactions, which prevents the conformational conversion of Aβ40 from the α-helix to β-sheet structure. By contrast, PSMα3 oligomers mainly combined with the central hydrophobic core (CHC) and the C-terminal region of the Aβ40 monomer by weak H-bonding and hydrophobic interactions, which could not inhibit the transition to the β-sheet structure in the aggregation pathway. Thus, the research has unraveled molecular interactions between Aβ40 and PSMα3 of different structures and provided a deeper understanding of the complex interactions between bacterial amyloids and AD-related pathogenic Aβ.