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Structure of the Chlamydia protein CADD reveals a redox enzyme that modulates host cell apoptosis

Robert Schwarzenbacher1, Frank Stenner-Liewen, Heike Liewen

  • 1The Burnham Institute, La Jolla, California 92037, USA.

The Journal of Biological Chemistry
|April 17, 2004
PubMed

Insights

Chlamydia protein CADD induces apoptosis by binding to host cell receptors. Its crystal structure reveals a redox-active site, suggesting dual mechanisms for its toxicity in Chlamydia infections.

Area of Science:

  • Molecular biology
  • Structural biology
  • Toxicology

Background:

  • Chlamydia protein CADD modulates host cell apoptosis.
  • CADD binds to death domains of tumor necrosis factor family receptors.
  • Transfection of CADD induces apoptosis in mammalian cells.

Purpose of the Study:

  • Determine the crystal structure of Chlamydia protein CADD.
  • Investigate the mechanism of CADD-induced apoptosis.
  • Elucidate the role of redox activity and death domain binding in CADD's function.

Main Methods:

  • X-ray crystallography to determine CADD structure.
  • Site-directed mutagenesis to create CADD mutants.
  • Apoptosis assays in mammalian cells.
  • Analysis of CADD's binding affinity to death domains.

Main Results:

  • CADD crystal structure reveals a dimer of seven-helix bundles with a di-iron center.
  • The active site resembles that of methane mono-oxygenase hydrolase.
  • Mutants lacking metal-coordinating residues showed reduced apoptosis induction but retained death domain binding.
  • CADD is identified as a novel redox protein toxin.

Conclusions:

  • CADD is a unique Chlamydia species toxin.
  • Both redox activity and death domain binding are essential for CADD's biological activity.
  • CADD represents a novel class of bacterial protein toxins.

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