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Crystal structure of the rac activator, Asef, reveals its autoinhibitory mechanism

Kazutaka Murayama1, Mikako Shirouzu2, Yoshihiro Kawasaki3

  • 1Tohoku University Biomedical Engineering Research Organization, Sendai 980-8575; RIKEN Genomic Sciences Center, Yokohama Institute, Yokohama 230-0045.

The Journal of Biological Chemistry
|December 28, 2006
PubMed

Insights

The Asef protein

Area of Science:

  • Molecular Biology
  • Biochemistry
  • Structural Biology

Background:

  • Adenomatous polyposis coli (APC) mutants in colorectal tumors activate the Rac-specific guanine nucleotide exchange factor (GEF), Asef.
  • Activated Asef promotes colorectal tumor cell migration.
  • Asef, like other Rho family GEFs, possesses Dbl homology (DH) and pleckstrin homology (PH) domains, but its autoinhibition mechanism is unknown.

Purpose of the Study:

  • To elucidate the three-dimensional structure of Asef in its autoinhibited state.
  • To identify the molecular mechanism underlying Asef autoinhibition.
  • To understand how the SH3 domain regulates Asef activity.

Main Methods:

  • X-ray crystallography to determine the three-dimensional structure of autoinhibited Asef.
  • Structural analysis to identify intramolecular interactions.
  • Analysis of domain interactions, including the SH3 domain with the DH domain.

Main Results:

  • The crystal structure revealed that the Src homology 3 (SH3) domain binds intramolecularly to the Dbl homology (DH) domain.
  • This SH3-DH interaction blocks the Rac-binding site, preventing Asef activation.
  • The SH3 domain interacts with the DH domain via its RT-loop and C-terminal region in a non-canonical manner.

Conclusions:

  • The SH3 domain's intramolecular binding to the DH domain is crucial for Asef autoinhibition.
  • This structural mechanism effectively blocks the Rac-binding site.
  • This autoinhibition mechanism may be conserved in other proteins containing adjacent SH3 and DH-PH domains.

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