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Interaction of MxiG with the cytosolic complex of the type III secretion system controls Shigella virulence

Nicola Barison1, Jutta Lambers, Robert Hurwitz

  • 1Department of Cellular Microbiology, Max-Planck-Institute for Infection Biology, Charitéplatz 1, 10117, Berlin, Germany.

FASEB Journal : Official Publication of the Federation of American Societies for Experimental Biology
|January 17, 2012
PubMed

Insights

Shigella flexneri

Area of Science:

  • Microbiology
  • Structural Biology
  • Molecular Biology

Background:

  • Gram-negative bacteria utilize the type 3 secretion system (T3SS) for host cell colonization.
  • The T3SS is a complex machinery responsible for translocating effector proteins into host cells.
  • Regulation of effector protein transport via the T3SS remains poorly understood.

Purpose of the Study:

  • To elucidate the structure and function of MxiG, a key component of the T3SS inner ring.
  • To investigate the regulatory mechanism of effector protein transport in Shigella flexneri.

Main Methods:

  • High-resolution X-ray crystallography of MxiG(1-126).
  • Pulldown assays and surface plasmon resonance to study protein interactions.
  • Cryo-electron microscopy (cryo-EM) for T3SS complex analysis.
  • Secretion assays and host cell invasion studies in Shigella knockout mutants.

Main Results:

  • The crystal structure of MxiG(1-126) reveals an FHA domain that binds phosphorylated threonines.
  • MxiG specifically interacts with the T3SS component Spa33 when phosphorylated.
  • Structural fitting shows MxiG's phosphoprotein binding site oriented towards the T3SS channel.
  • Phosphoprotein binding of MxiG is crucial for bacterial virulence and T3SS regulation.

Conclusions:

  • MxiG acts as a regulator of the type 3 secretion system in Shigella flexneri.
  • Phosphorylation-dependent binding of MxiG to Spa33 is essential for T3SS function and bacterial pathogenesis.
  • This study provides structural insights into the T3SS regulatory mechanism.

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