Isolation and characterization of a calmodulin binding fragment of chicken gizzard caldesmon

A calmodulin binding portion was separated from chicken gizzard caldesmon by chymotryptic digestion and it was purified through two column chromatography steps on calmodulin-Sepharose and Ultrogel AcA 44. The isolated fragment has an estimated molecular weight of 35,000 (35K) and it was possibly derived from the C-terminal portion of caldesmon. The affinity of the 35K fragment for calmodulin was determined by using the characteristic calmodulin-dependent mobility shift in polyacrylamide gel electrophoresis. The 35K fragment retained the actin binding site of caldesmon. The interaction of the 35K fragment with actin was released in the presence of Ca2+ and calmodulin.