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Structural basis of cytotoxicity mediated by the type III secretion toxin ExoU from Pseudomonas aeruginosa

Claire Gendrin1, Carlos Contreras-Martel, Stéphanie Bouillot

  • 1Bacterial Pathogenesis Group, Institut de Biologie Structurale-IBS, Université Grenoble I, Grenoble, France.

Plos Pathogens
|April 13, 2012
PubMed

Insights

The Pseudomonas aeruginosa type III secretion system (T3SS) toxin ExoU rapidly causes cell death. Its crystal structure reveals a phospholipase domain requiring conformational changes to access membrane lipids, potentially targeted for degradation.

Area of Science:

  • Microbiology
  • Structural Biology
  • Cell Biology

Background:

  • The type III secretion system (T3SS) is a critical virulence factor for Gram-negative pathogens.
  • ExoU, a potent phospholipase toxin from Pseudomonas aeruginosa, induces rapid host cell necrosis.
  • Understanding ExoU's structure and function is crucial for developing therapeutic strategies.

Purpose of the Study:

  • To determine the crystal structure of ExoU in complex with its chaperone SpcU.
  • To elucidate the structural basis for ExoU's membrane interaction and phospholipase activity.
  • To investigate the cellular fate of ExoU upon ubiquitination.

Main Methods:

  • X-ray crystallography to obtain the ExoU-SpcU complex structure.
  • Domain analysis of ExoU structure (membrane-binding, bridging, phospholipase).
  • Cell-based assays (transfection, bacterial infection) to study ExoU localization and ubiquitination.

Main Results:

  • The crystal structure revealed ExoU's distinct domains and SpcU's role in maintaining ExoU secretion-competency.
  • The phospholipase domain's catalytic site is inaccessible, suggesting a conformational change is needed for lipid interaction.
  • ExoU ubiquitination leads to co-localization with endosomal markers, indicating a host defense mechanism.

Conclusions:

  • The ExoU structure provides insights into its mechanism of action and regulation by SpcU.
  • ExoU likely undergoes conformational rearrangements to engage membrane lipids.
  • Host cell ubiquitination may target ExoU for degradation, mitigating its cytotoxic effects.

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