STRUCTURAL AND FUNCTIONAL-CHARACTERIZATION OF CALELECTRINS FROM BOVINE LIVER

Two Ca2+-dependent membrane-binding proteins with apparent molecular weights of 70000 (calelectrin70) and 32000 (calelectrin32) were isolated from bovine liver using phenyl-Sepharose affinity chromatography followed by diethylaminoethyl (DEAE)-cellulose and Ultrogel AcA44 chromatographies. Limited proteolysis and immunological analyses indicated that calelectrin32 was not a digested product from calelectrin70. Both calelectrins bound to phosphatidylserine and to calmodulin in a Ca2+-dependent manner. Circular dichroism studies showed that the apparent alpha-helical contents of calelectrin70 and calelectrin32 were 25 and 40%, respectively and they underwent Ca2+-dependent conformational changes. When the calelectrins were incubated with a brain microtubule preparation, they were phosphorylated by endogenous kinase(s) and phosphorylation occurred on serine residues. Moreover, calelectrin70 showed an inhibitory action on endogenous kinase activity in the presence of Ca2+.