Phenol-soluble modulins (PSMs) are a family of small proteins, that carry out a variety of functions, including acting as toxins, assisting in biofilm formation, and colony spreading.
Many PSMs are encoded within the core genome and can play an important virulence factor.
[1] PSMs were first discovered in S. epidermidis by Seymour Klebanoff via hot-phenol extraction and were described as a pro-inflammatory complex of three peptides.
However, due in part to the small size of many PSMs, they have largely gone unnoticed until recent years.
PSMα forms an amphipathic α-helix structure that composes the entire length of the peptide.
[2] PSM-mec RNA has been implicated in the regulation of the agr system and as a result can influence the expression of other PSMs.
[3] In addition the MgrA system has been shown to alter biofilm formation, via suppression of PSMs.
[4] The environment S. aureus is exposed to has been demonstrated to play a role in PSM expression.
[6] In addition to their pro-inflammatory properties, PSMs have been shown to be directly sensed by circulating leucocytes through the formyl peptide receptor FPR2, thus driving a rapid, pathogen-specific attraction of neutrophiles to the site of infection, via an EGR1-dependent signalling pathway.
It has been demonstrated that secreted PSMs are able to induce Neutrophil Extracellular Trap release.
Many PSMs have cytolytic activity and play a major role in the nonspecific lysing of host cells, including Polymorphonuclear Leukocytes (PMNs).
[2] The aggregation of α-type PSMs into fibrils is able to modulate S. aureus biofilm formation.
[2] Altering the structure of PSMβ has been demonstrated to disrupt their ability to influence biofilm formation.