Structural Insights into Curli CsgA Cross-β Fibril Architecture Inspire Repurposing of Anti-amyloid Compounds as Anti-biofilm Agents

Abstract

Curli amyloid fibrils secreted by Enterobacteriaceae mediate host cell adhesion and contribute to biofilm formation, thereby promoting bacterial resistance to environmental stressors. Here, we present crystal structures of amyloid-forming segments from the major curli subunit, CsgA, revealing steric zipper fibrils of tightly mated β-sheets, demonstrating a structural link between curli and human pathological amyloids. D-enantiomeric peptides, originally developed to interfere with Alzheimer’s disease-associated amyloid-β, inhibited CsgA fibrillation and reduced biofilm formation in Salmonella typhimurium. Moreover, as previously shown, CsgA fibrils cross-seeded fibrillation of amyloid-β, providing support for the proposed structural resemblance and potential for cross-species amyloid interactions. The presented findings provide structural insights into amyloidogenic regions important for curli formation, suggest a novel strategy for disrupting amyloid-structured biofilms, and hypothesize on the formation of self-propagating prion-like species originating from a microbial source that could influence neurodegenerative diseases.

What Are the Molecular Mechanisms by Which Functional Bacterial Amyloids Influence Amyloid Beta Deposition and Neuroinflammation in Neurodegenerative Disorders?

“…That is, a bacterial amyloid protein may influence the aggregation of neuronal proteins. Perov et al discovered structural similarity between the fibers of the best studied bacterial amyloid protein curli, and neuronal amyloids [14]. They noted that the curli protein CsgA cross-seeds the fibrillation of Aβ, as was previously proposed [10].…”

“…It has been observed that protein folding in an amyloid configuration is a highly conserved process throughout evolution [14]. Recently, a series of studies have shown that FUBAs may interact with neuronal proteins in the manner predicted.…”

Salmonella Typhimurium biofilm disruption by a human antibody that binds a pan-amyloid epitope on curli

“…Curli amyloid shares structural and functional features with non-bacterial amyloids. Atomic resolution imaging revealed that curli amyloid fibrils resemble the Aβ fibrils found in Alzheimer's disease 53 , and synthetic D-enantiomeric peptides designed to inhibit Aβ fibrillization also inhibit CsgA fibrillation. Curli fibrillization is also inhibited by human transthyretin, an amyloid protein responsible for cardiomyopathy and neuropathy 54 .…”

Intercellular transmission of a bacterial cytotoxic prion-like protein in mammalian cells

“…It is noteworthy that, under our experimental conditions, the uptake of recombinant WH1(A31V) amyloids by cells not expressing WH1(WT), but just the fluorescent proteins to which the prion-like protein was tagged, does not result in any evident toxicity for the recipient cells. Although there is no protein with a noticeable degree of sequence identity with RepA-WH1 in the human proteome (BLAST best match E-value = 0.11), it has been recently suggested that bacterial extracellular amyloids may template amyloidogenesis on human proteins implicated in neurodegeneration in spite of the lack of significant sequence similarities (Friedland and Chapman, 2017; Perov et al, 2019). This could constitute a matter of concern on the biosafety of bacterial amyloids.…”