Amyloid transformations of phenol soluble modulin α1 in Staphylococcus aureus and their modulation deploying a prenylated chalcone.

Phenol soluble modulins (PSMs) are small amphipathic peptides involved in a series of biological functions governing staphylococcal pathogenesis, primarily by facilitating the formation of an extracellular fibril structure with amyloid-like properties. This fibrillar architecture stabilizes the staphylococcal biofilm making it resilient to antibiotic treatment. Our study aims to abrogate the amyloid fibrillation of PSM α1 with novel insights on the amyloid modulatory potential of a prenylated chalcone, Isobavachalcone (IBC). A combination of biophysical and computational assays to address the amyloid modulatory effect of IBC has been undertaken to arrive at a model for the inhibition of PSM α1 fibrillation. ThT kinetics studies indicated that IBC must be stably interacting with the amyloidogenic core of PSM α1 monomers or it may be inhibiting the pre-fibrillar aggregates populated at the early stages of amyloid transformation kinetics. This heteromolecular association further inhibits the amyloid transformation corroborated by a ∼ 94% and ∼ 91% reduction in the ThT maxima, even at sub-stoichiometric concentrations. Transmission electron microscopy (TEM) of end-stage aggregates (∼ 55 h) depict mature, inter-twined, laterally stacked amyloid fibrils in untreated PSM α1 samples while this fibrillar load is remarkably reduced in the presence of IBC. The inhibitory effect of IBC on the β-sheet transitions of PSM α1 were also validated using far-UV CD spectra. Molecular dynamics simulation studies with PSM aggregates (PSM-A) have also suggested that IBC disrupts the hydrogen bonding interactions and corroborates the inhibition of alpha to beta transitions of PSM-A. Collectively, our data proposes a novel structural motif for the rational discovery of non-toxic therapeutic agents targeting the functional amyloids which have slowly emerged as potent factors, consolidating the antibiotic resistant staphylococcal biofilm assembly.