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Ca²+-induced release of mitochondrial m-calpain from outer membrane with binding of calpain small subunit and Grp75

Taku Ozaki1, Tetsuro Yamashita, Sei-ichi Ishiguro

  • 1Department of Biochemistry and Biotechnology, Faculty of Agriculture and Life Science, Hirosaki University, Hirosaki 036-8561, Japan.

Archives of Biochemistry and Biophysics
|December 15, 2010
PubMed

Insights

Mitochondrial outer membrane calpains are activated by their small subunit, releasing the large subunit and facilitating apoptosis. This study uncovers the mechanism of calpain activation in cell death.

Area of Science:

  • Cell Biology
  • Biochemistry
  • Molecular Biology

Background:

  • Mitochondrial calpains (μ- and m-calpains) are crucial in apoptosis.
  • The precise mechanisms activating these calpains at the mitochondrial outer membrane (OM) remain unclear.

Purpose of the Study:

  • To elucidate the core factors responsible for activating mitochondrial OM-bound calpains.
  • To understand the mechanism of OM-bound calpain release from the mitochondrial outer membrane.

Main Methods:

  • Solubilization and DEAE-Sepharose column chromatography of OM-bound calpains.
  • Identification via immunoblots.
  • Calpain assays, immunoprecipitations, and immunoblots to determine activating factors and release mechanisms.

Main Results:

  • The OM-bound m-calpain large subunit was found independent of the small subunit and Grp75 chaperone.
  • Free calpain small subunit, located in the intermembrane space (IMS), triggered the release of the OM-bound m-calpain large subunit.
  • This release involved Grp75, ATP, and Ca²+.

Conclusions:

  • The activation mechanism of mitochondrial OM-bound m-calpain involves its free small subunit.
  • The release of mitochondrial m-calpain from the OM is a key event in facilitating apoptotic cell death.

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