Sequence variations govern the hierarchical self-assembly and structural polymorphism of PSM-α functional amyloids

Biofilm-associated functional amyloids reinforce extracellular matrices and enhance microbial resistance to environmental and antimicrobial stresses. In Staphylococcus aureus, phenol-soluble modulins (PSMs), particularly the PSM-α family, regulate biofilm maturation and pathogenicity through sequence-dependent self-assembly. However, how subtle sequence variations encode distinct conformational landscapes and supramolecular architectures remains unclear. Here, we combined atomistic discrete molecular dynamics (DMD) and coarse-grained (CG) simulations with all-atom MD refinement to elucidate PSM-α self-assembly. PSM-α1, PSM-α2, and PSM-α4 monomers sampled heterogeneous ensembles with pronounced β-sheet propensities and underwent disorder-to-β-sheet transitions upon self-assembly. Notably, their conserved ⁷IIKXI¹¹ region exhibited the highest β-sheet propensity and inter-peptide backbone contact frequencies, identifying it as a major β-sheet-forming hotspot within the experimentally established amyloidogenic region. In contrast, PSM-α3 intrinsically favored an amphipathic α-helical ensemble and retained its helical organization during assembly through lateral association of preformed helices. CG simulations followed by unrestrained all-atom MD refinement further revealed distinct higher-order architectures and confirmed their structural stability. Collectively, these findings link sequence variation to PSM-α structural polymorphism and highlight the conserved ⁷IIKXI¹¹ region as a potential target for disrupting amyloid assembly and developing anti-biofilm strategies.