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Rgg protein structure-function and inhibition by cyclic peptide compounds.

Vijay Parashar1, Chaitanya Aggarwal2, Michael J Federle2

  • 1Department of Microbiology, Biochemistry, and Molecular Genetics, New Jersey Medical School, Rutgers, The State University of New Jersey, Newark, NJ 07103; and.

Proceedings of the National Academy of Sciences of the United States of America
|April 8, 2015
PubMed
Summary

Structural insights into Rgg protein function reveal how cyclosporin A and valspodar inhibit peptide pheromone signaling in Firmicutes. A unique disulfide bond in the DNA-binding domain may regulate Rgg protein activity.

Keywords:
Rgg proteinSHP pheromoneStreptococcuscyclosporin Aquorum sensing

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Area of Science:

  • Microbiology
  • Structural Biology
  • Biochemistry

Background:

  • Peptide pheromone cell-cell signaling, or quorum sensing, controls phenotypes like virulence in Firmicutes, including pathogens such as Streptococcus species.
  • Rgg proteins are crucial cytoplasmic transcription factors acting as peptide pheromone receptors in Firmicutes.

Purpose of the Study:

  • To determine the X-ray crystal structures of a Streptococcus Rgg protein.
  • To elucidate the mechanism of inhibition by cyclosporin A and its analog valspodar.
  • To investigate the structural basis for Rgg protein dimerization and potential redox regulation.

Main Methods:

  • X-ray crystallography was used to obtain structures of an Rgg protein alone and complexed with cyclosporin A.
  • Structure-function analysis was performed to identify the peptide pheromone-binding site and inhibition mechanism.
  • Inhibition assays were conducted using cyclosporin A and valspodar on Rgg proteins from relevant Streptococcus species.

Main Results:

  • The first X-ray crystal structures of an Rgg protein were determined, revealing the peptide pheromone-binding site.
  • Cyclosporin A was shown to inhibit Rgg protein activation by binding to the receptor.
  • Valspodar was identified as an inhibitor of Rgg activation in Streptococcus species.
  • A unique intermolecular disulfide bond was discovered linking the DNA-binding domains of the Rgg protein.

Conclusions:

  • The crystal structures provide a mechanistic understanding of Rgg protein inhibition by signaling antagonists.
  • Valspodar represents a potential therapeutic lead for targeting Rgg-mediated processes in Streptococcus infections.
  • The disulfide bond may play a role in regulating Rgg protein conformation, dimerization, or activity through redox control.