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Identification of a major, CsrRS-regulated secreted protein of Group A streptococcus

A Heath1, A Miller, V J DiRita

  • 1Department of Internal Medicine, University of Michigan School of Medicine, Ann Arbor, MI 48109, U.S.A.

Microbial Pathogenesis
|July 17, 2001
PubMed

Insights

Researchers identified a new Group A Streptococcus protein, MspA, regulated by CsrR/CsrS. Deleting mspA did not impact virulence or capsule expression in mouse skin infections.

Area of Science:

  • Microbiology
  • Molecular Biology
  • Bacterial Pathogenesis

Background:

  • The CsrR/CsrS two-component system regulates extracellular virulence factors in Group A Streptococcus.
  • The complete set of exoproteins controlled by CsrR/CsrS remains largely unknown.

Purpose of the Study:

  • To identify novel exoproteins regulated by the CsrR/CsrS system in Group A Streptococcus.
  • To characterize a newly identified 23 kDa secreted protein, designated MspA.

Main Methods:

  • Comparative analysis of culture supernates from wild-type and CsrR mutant strains using two-dimensional gel electrophoresis (2DGE).
  • N-terminal sequencing and identification of a putative open reading frame (ORF).
  • Mobility shift assays to confirm CsrR binding and primer extension analysis for gene expression studies.

Main Results:

  • A previously unidentified 23 kDa protein, MspA, was found in supernates of DeltacsrRS(-) mutant strains but not wild-type.
  • CsrR directly binds to the promoter region of the mspA gene.
  • MspA is expressed during mid- and late-exponential phases in a DeltacsrRS(-) mutant.
  • Deletion of mspA did not affect colony morphology, mucoidy, in vitro growth, or virulence in a mouse skin infection model.
  • MspA is co-regulated with other virulence factors but its absence does not alter hyaluronic acid capsule expression or infection severity.

Conclusions:

  • CsrR/CsrS regulates the expression of a novel secreted protein, MspA, in Group A Streptococcus.
  • MspA is not essential for Group A Streptococcus virulence in a mouse skin infection model.
  • The role of MspA in streptococcal pathogenesis requires further investigation.

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