Functional domain of caldesmon.

Limited proteolysis of caldesmon has been used in studying the structure-function relationship of this protein. Digestion with alpha-chymotrypsin yields three major fragments of 110, 80 and 40 kDa. Only the 40 kDa fragment preserves functional properties of the parent molecule: it binds to F-actin, causes inhibition of actomyosin ATPase and binds to calmodulin in a Ca2+-dependent manner. Its further degradation produces an 18 kDa polypeptide that also retains all these properties. Neither F-actin nor calmodulin binding induces dramatic changes in susceptibility to chymotryptic cleavage and the sites of cleavage of caldesmon.