Phenol Soluble Modulin (PSM) Variants of Community-Associated Methicillin-Resistant Staphylococcus aureus (MRSA) Captured Using Mass Spectrometry-Based Molecular Networking

Abstract

Molecular genetic analysis indicates that the problematic human bacterial pathogen methicillin-resistant Staphylococcus aureus possesses more than 2000 open reading frames in its genome. This number of potential gene products, coupled with intrinsic mechanisms of posttranslational modification, endows methicillin-resistant Staphylococcus aureus with a highly complex biochemical repertoire. Recent proteomic and metabolomic advances have provided methodologies to better understand and characterize the biosynthetic factors released by microbial organisms. Here, the emerging tool of mass spectrometry-based molecular networking was used to visualize and map the repertoire of biosynthetic factors produced by a community-associated methicillin-resistant Staphylococcus aureus strain representative of the epidemic USA300 clone. In particular, the study focused on elucidating the complexity of the recently discovered phenol soluble modulin family of peptides when placed under various antibiotic treatment stresses. Novel PSM truncated variant peptides were captured, and the type of variants that were clustered by the molecular networks platform changed in response to the different antibiotic treatment conditions. After discovery, a group of the peptides were selected for functional analysis in vitro. The peptides displayed bioactive properties including the ability to induce proinflammatory responses in human THP-1 monocytes. Additionally, the tested peptides did not display antimicrobial activity as previously reported for other phenol soluble modulin truncated variants. Our findings reveal that the PSM family of peptides are quite structurally diverse, and suggest a single phenol soluble modulin parent peptide can functionally spawn differential bioactivities in response to various external stimuli. Molecular & Cellular Proteomics

Natural products as mediators of disease

“…78 Intriguingly, treatment of S. aureus with antibiotics leads to the production of PSM structural variations via truncation of the peptide and amino acid substitutions. 77 Production concentrations of PSMs are much lower from the S. aureus related commensal species Staphylococcus epidermidis , explaining its reduced virulence. 81 It has been suggested that some strains of S. epidermidis may inhibit potential pathogens by enhancing production of human antimicrobial peptides.…”

The Human LL-37(17-29) Antimicrobial Peptide Reveals a Functional Supramolecular Nanostructure

“…Although originating from different organisms, PSMα3 and hLL-37 display sequence homology, particularly in their core region ( Fig. S1) and are cleaved in-vivo into active derivatives (36)(37)(38)(39)(40)(41)(42). Many hLL-37 derivatives show a diverse array of selectivity against microbial strains, and additional functions within the immune system (26,36,37,43,44).…”

N-Terminal ArgD Peptides from the Classical Staphylococcus aureus Agr System Have Cytotoxic and Proinflammatory Activities

“…Recently, our group used the platform to build a molecular network representative of extracellularly released, small molecular weight biosynthetic factors produced by MRSA (Gonzalez et al, 2014). Here, we report the continued examination of the created molecular network by de novo sequencing and peptidogenomic approaches (Kersten et al, 2011), recovering peptides pertaining to the AgrD N-terminal domain ( Figure S1 ).…”

“…PSMs are cytolytic, formylated and non-formylated peptide variants that are upregulated in community-associated MRSA and genetically linked to the agr system (PSMγ is embedded within RNA III) (Wang et al, 2007; Gonzalez et al, 2014). Because of the structural similarities between peptides, N-AgrD could play a potential role in biofilm structural formation as demonstrated for PSMs (Periasamy et al, 2012).…”