Biology subjects

Rayan, B.

Publications and source records attributed to Rayan, B..

4 recordsLinked to original sources

bioRxiv2026

Structural and Functional Plasticity of the Staphylococcus aureus Virulence-Associated Amyloid Peptide PSMα1

Phenol-soluble modulin 1 (PSM1) is a cytolytic peptide secreted by Staphylococcus aureus that contributes to host-cell damage and biofilm stability, yet the relationship between its assembly behavior and function remains incompletely understood. Here, we combine cellular assays, molecular spectroscopy, and high-resolution structural approaches to elucidate how environmental conditions govern PSM1 activity and supramolecular organization. Live-cell imaging and cytotoxicity assays show that PSM1 accumulates at the plasma membrane of human cells prior to membrane permeabilization, linking membrane association to cytotoxic outcomes. This process is strongly attenuated by epigallocatechin gallate (EGCG). Cryogenic electron microscopy (cryo-EM) reveals two polymorphic canonical amyloid fibril architectures that share a conserved hydrophobic core and protofilament interface. In parallel, we identify pH as a key determinant of PSM1 assembly pathways, driving a bifurcation between cross-{beta} amyloid fibrils at extreme acidic and alkaline conditions and heterogeneous, long-lived, thermally stable -helical nanotubular assemblies at acidic, near-neutral, and slightly alkaline conditions, which act as transient intermediates under highly acidic conditions. Together, these findings demonstrate that PSM1 is not a single amyloid structure but a condition-dependent structural system in which environmental cues dictate assembly, membrane interaction, and cytotoxic function. This work provides a framework for understanding how polymorphic assembly of bacterial virulence peptides interfaces with host-cell interactions and suggests new avenues for targeting PSM-mediated pathogenicity. Statement of significanceStaphylococcus aureus causes severe infections and uses the peptide PSM1 to damage host cells and strengthen protective biofilms. Like many disease-associated proteins, PSM1 self-assembles into amyloid fibrils, though their role in virulence remains unclear. We show that PSM1 does not adopt a single architecture. Instead, environmental changes, such as those at infection sites, drive the peptide into distinct assemblies, including cross-{beta} amyloid fibrils and unexpectedly stable nanotubes with -helical features. Live-cell imaging shows PSM1 accumulates at the plasma membrane before cell death, and that epigallocatechin gallate reduces membrane association and toxicity. These findings show that bacterial virulence can be regulated through environmentally controlled transitions between protein assemblies, identifying membrane accumulation as a promising anti-virulence target.

biophysics↗

bioRxiv2025

RNA Selectively Modulates Activity of Virulent Amyloid PSMα3 and Host Defense LL-37 via Phase Separation and Aggregation Dynamics

Amyloid-forming peptides are increasingly recognized as dynamic regulators at the host-pathogen interface, yet how environmental factors control their assembly and activity remains poorly understood. Here, RNA acts as a concentration-dependent regulator of two sequence-related -helical peptides with fundamentally different assembly behaviors: the cross- amyloid-forming Staphylococcus aureus virulence factor PSM3 and the non-amyloidogenic human host-defense peptide LL-37. RNA drives PSM3 through distinct assembly states, from liquid-like condensates to fibrillar polymorphs, while preserving cytotoxic and antimicrobial activity over time. In contrast, RNA attenuates LL-37 cytotoxicity toward host cells while maintaining antibacterial activity, consistent with a host-protective immunomodulatory effect. Together with the opposing effects of EGCG, which redirects both peptides into amorphous assemblies, these findings support a mechanistic model in which biological activity is governed by supramolecular architecture, assembly trajectory, and dynamics rather than by monomer abundance or mature fibrils alone. More broadly, our findings identify RNA as an environmental regulator of -helical peptide assemblies and establish assembly-state control as a tunable determinant of virulence and host defense.

biophysics↗

bioRxiv2025

Structural and Functional Versatility of the Amyloidogenic Antimicrobial Peptide Citropin 1.3

Citropin 1.3 is an antimicrobial peptide produced by the amphibian Litoria citropa (Southern bell frog), which self-aggregates into distinct fibrillar structures, however, the function of the fibrils remains unclear and largely unexplored. In this study, the structural and functional properties of citropin 1.3 were investigated using cryogenic electron microscopy and fluorescence microscopy in the presence of membrane and cell models, and with X-ray crystallography. Canonical amyloids, multilayered nanotubes, and a novel mixed fibril were observed. Experiments with negatively charged giant unilamellar vesicles revealed that the peptide facilitates membrane fusion while simultaneously undergoing phase separation in the presence of phospholipids. In presence of mammalian cells, citropin 1.3 permeabilizes membranes, leading to cell death, and over time, colocalizes with genetic material. Overall, this work provides new insights into the structural dynamics of the amyloidogenic antimicrobial peptide citropin 1.3 and its interactions with different systems.

molecular biology↗

bioRxiv2022

Natural Antimicrobial Peptides Self-assemble as α/β Chameleon Amyloids

Amyloid protein fibrils and some antimicrobial peptides (AMPs) share biophysical and structural properties. This observation suggests that ordered self-assembly can act as an AMP-regulating mechanism, and, vice versa, that human amyloids play a role in host defense against pathogens, as opposed to their common association with neurodegenerative and systemic diseases. Based on previous structural information on toxic amyloid peptides, we developed a sequence-based bioinformatics platform and, led by its predictions, experimentally identified 14 fibril-forming AMPs (ffAMPs) from living organisms, which demonstrated cross-{beta} and cross- amyloid properties. The results support the amyloid-antimicrobial link. The high prevalence of ffAMPs produced by amphibians and marine creatures among other species suggests that they confer unique advantageous properties in distinctive environments, potentially providing stability and adherence properties. Most of the newly identified 14 ffAMPs showed lipid-induced and/or time-dependent secondary structure transitions in the fibril form, indicating structural and functional cross-/{beta} chameleons. Specifically, ffAMP cytotoxicity against human cells correlated with inherent or lipid-induced -helical fibril structure. The findings raise hypotheses about the role of fibril secondary structure switching in regulation of processes, such as the transition between a stable storage conformation and an active state with toxicity against specific cell types.

biophysics↗