Calpain Subunits Remain Associated during Catalysis

Authors: Zhang W.; Mellgren R.L.

Source: Biochemical and Biophysical Research Communications, Volume 227, Number 3, October 1996 , pp. 890-896(7)

Publisher: Academic Press

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Abstract:

The Ca 2+ dependent cysteine proteases, calpains, are heterodimers containing a large ( ca. 80 kDa) catalytic subunit and a 25-30 kDa small subunit. Whether calpains remain dimers while catalyzing hydrolysis of protein substrates has been controversial. Now by doing subunit co-immunoprecipitation, we provide direct evidence to resolve this argument. In the presence of Ca 2+ concentrations which permit catalytic activity, both subunits of either m- or mu-calpain are co-immunoprecipitated by monoclonal antibodies directed against a single subunit. Furthermore, both subunits can be co-immunoprecipitated during calpain-catalyzed proteolysis of the substrate casein. These results indicate that both major calpain isozymes maintain their heterodimeric form during the catalytic cycle. Thus, small subunit might have a direct role in regulating the physiologic function of either major calpain isozyme.

Language: English

Document Type: Research article

Affiliations: Department of Pharmacology and Therapeutics, Medical College of Ohio, Toledo, Ohio, 43699-0008:

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