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Identification of a Bcl-XL binding region within the ATPase domain of Apaf-1

Hirohiko Yajima1, Fumio Suzuki

  • 1Department of Molecular Radiobiology, Research Institute for Radiation Biology and Medicine, Hiroshima University, Hiroshima 734-8553, Japan. yajima@hiroshima-u.ac.jp

Biochemical and Biophysical Research Communications
|September 10, 2003
PubMed

Insights

Bcl-XL directly binds to a specific region of Apaf-1, the Bcl-XL binding region (BBR). This interaction is crucial for regulating apoptosis, similar to the C. elegans CED-9/CED-4 pathway.

Area of Science:

  • Molecular Biology
  • Cell Biology
  • Biochemistry

Background:

  • The pro-apoptotic factor CED-4 in C. elegans activates CED-3 protease, with CED-9 inhibiting this function through direct binding.
  • The mammalian homologues are Bcl-XL (CED-9) and Apaf-1 (CED-4), but their direct interaction remained unconfirmed.

Purpose of the Study:

  • To investigate whether the mammalian Bcl-XL homologue directly binds to and inhibits Apaf-1, analogous to the CED-9/CED-4 interaction.

Main Methods:

  • Yeast two-hybrid system was employed to analyze protein interactions.
  • Fragment libraries of bcl-XL and apaf-1 cDNA were created and screened.
  • Immunoprecipitation assays were used to confirm binding.

Main Results:

  • Nine Apaf-1 fragments interacting with Bcl-XL were identified, all containing the Bcl-XL binding region (BBR) within the ATPase domain.
  • Direct binding of BBR to Bcl-XL was confirmed via immunoprecipitation.
  • Other Bcl-2 family members (Bcl-2, Bcl-w, A1/Bfl-1, Boo/Diva) did not bind BBR as effectively as Bcl-XL.

Conclusions:

  • Bcl-XL directly binds to a specific region (BBR) in Apaf-1.
  • This direct interaction provides mechanistic insight into apoptosis regulation in mammals.

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