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Group A Streptococcal M1 Protein Sequesters Cathelicidin to Evade Innate Immune Killing

Christopher N LaRock1, Simon Döhrmann1, Jordan Todd1

  • 1Department of Pediatrics, University of California, San Diego, La Jolla, CA 92093, USA.

Cell Host & Microbe
|October 16, 2015
PubMed

Insights

Group A Streptococcus (GAS) uses its M1 protein to neutralize the antimicrobial peptide LL-37, evading immune defenses. This resistance mechanism is crucial for the pathogen

Area of Science:

  • Microbiology
  • Immunology
  • Pathogenesis

Background:

  • The antimicrobial peptide LL-37 is a key component of the innate immune system, targeting pathogens.
  • Certain Group A Streptococcus (GAS) strains, particularly the hypervirulent M1T1 serogroup, exhibit resistance to LL-37.
  • Understanding resistance mechanisms is vital for combating invasive bacterial infections.

Purpose of the Study:

  • To investigate how hypervirulent M1T1 GAS evades LL-37-mediated antimicrobial activity.
  • To elucidate the role of the GAS M1 protein in neutralizing LL-37 and its precursor.
  • To determine the contribution of LL-37 resistance to GAS pathogenesis.

Main Methods:

  • In vitro assays to assess LL-37 and cathelicidin binding by the M1 protein.
  • Analysis of M1 protein's effect on LL-37 antimicrobial and chemotactic functions.
  • In vivo studies using a murine model of necrotizing skin infection to evaluate M1-mediated virulence.

Main Results:

  • The GAS M1 protein directly sequesters and neutralizes human LL-37 via its N-terminal domain.
  • M1 protein prevents the maturation of the LL-37 precursor (hCAP-18).
  • Exogenous M1 protein protects GAS from neutrophil killing and LL-37's immune-stimulating effects.
  • M1 protein neutralizes murine cathelicidin, contributing to virulence in a mouse model.

Conclusions:

  • Cathelicidin resistance, mediated by the M1 protein, is essential for the pathogenesis of hyperinvasive M1T1 GAS.
  • The M1 protein's ability to neutralize host defense peptides is a critical virulence factor.
  • Targeting this resistance mechanism could offer new therapeutic strategies against invasive GAS infections.

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