# Contribution of the peptidome to CA-MRSA virulence

> **NIH NIH R01** · UNIVERSITY OF CALIFORNIA, SAN DIEGO · 2021 · $394,792

## Abstract

PROJECT SUMMARY
A comprehensive understanding of bacterial pathogenesis not only requires a detailed knowledge of the
genome and proteome, but also the peptidome elaborated during the progression of infection. The overall
objective of this proposal is to build upon our exciting preliminary observations describing the identification of
endogenous microproteins and peptides detected in cell-free supernatants of community-associated (CA)
MRSA cultures. Within this group we identified two novel microproteins originating from an unannotated locus
in the CA-MRSA TCH1516 genome. We found that these microproteins, termed S. aureus microprotein 1
(SAM1) and S. aureus microprotein 2 (SAM2), are highly conserved among Staphylococci and are regulated
by the classical accessory gene regulatory system. We have started to characterize these factors, showing that
SAM1 appears to act as a canonical cytolysin. Intriguingly, SAM2 possesses unique bioactivity, the
perturbation of keratin networks that promotes an in vivo switch from a localized S. aureus skin infection to an
invasive dissemination to the underlying tissues. The central hypothesis of this proposal is that SAMs
significantly contribute to CA-MRSA’s ability to cause disease in a host. In Aim 1, we will dissect the
pathogenic contributions of SAM1 as a functional cytolysin in vitro and in vivo. Given the bioactivity of SAM1 is
inhibited by serum lipoproteins, we will focus on its role once CA-MRSA is in an intracellular environment. Our
strong preliminary data suggests SAM1 selectively binds to prohibitins (PHBs) across differential host cell
types. Thus, we will take the study of CA-MRSA cytolysins in a new direction by dissecting the potential role of
PHBs as targets of SAM1. In Aim 2, we will perform a structure and function analysis of the interaction
between SAM2 and keratin. Our data shows that this interaction has an important in vivo consequence during
the shift from a local to invasive infection type. By a powerful combination of microbiology and multi-omic
approaches, we will define the SAM2 structural contact points required for pathogenesis and will detail host
pathways that are impacted by SAM2 during the invasive switch. In Aim 3, to assess the broader significance
of our discovery, we will determine the pathogenic roles SAMs play in a diverse library of CA-MRSA strains, in
addition to other Staphylococcal pathogens that express bioactive SAM homologs. Aim 3 is critical given that
the importance of SAMs in other Staphylococci beyond CA-MRSA TCH1516 remains unknown. This proposal
is highly innovative because it departs from the current focus of investigating host-pathogen interactions
through the more established genomic and proteomic workflows. The proposed work is highly significant given
it can drive the development of anti-Staphylococcal therapies based on a relatively new and largely mysterious
molecular paradigm - the peptidome.

## Key facts

- **NIH application ID:** 10166766
- **Project number:** 5R01AI148417-02
- **Recipient organization:** UNIVERSITY OF CALIFORNIA, SAN DIEGO
- **Principal Investigator:** David J Gonzalez
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $394,792
- **Award type:** 5
- **Project period:** 2020-05-18 → 2025-04-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10166766

## Citation

> US National Institutes of Health, RePORTER application 10166766, Contribution of the peptidome to CA-MRSA virulence (5R01AI148417-02). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/10166766. Licensed CC0.

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