CALMODULIN PREVENTS THE PROTEOLYSIS OF CONNEXIN32 BY M-CALPAIN

Purified mouse liver gap junctions formed by connexin32 and connexin26 were treated with the low Ca2+-affinity isoform of calpain (m-calpain ). This protease proteolyzes connexin32 but not connexin26. However, t he binding of calmodulin to connexin32 prevented its proteolysis. Conn exin32, but not connexin26, was phosphorylated by protein kinase A, an d calmodulin bound to the phosphorylated form of connexin32 also prote cted the latter against m-calpain-mediated proteolysis. We propose tha t calmodulin plays a modulatory role on the degradation of connexin32 and hence on the turnover of gap junction channels. (C) 1997 Elsevier Science S.A.