Purification and Characterization of a Novel 160kDa Actin-Binding Protein from Surf Clam Foot Muscle

Abstract

A 160kDa actin-binding protein was isolated from surf clam foot muscle by DEAE-Toyopearl column chromatography. The protein was found to complex readily with F-actin to form turbidity. The turbidity reached a maximum when bound in a ratio of approx. 0.3:1 (w/w). The binding ratio as well as turbidity decreased steeply as the KCl increased concentration up to 80-100mM. In these events, F-actin filaments were aggregated side by side and formed complicated networks, whose morphological features revealed close similarity to those reported for F-actin bundles formed by caldesmon. However, the binding features of the 160kDa protein to F-actin are different from those with caldesmon in the presence of Ca²⁺-calmodulin. Besides, further comparison of molecular weights, amino acid compositions, and α-helix contents revealed that the 160kDa protein is different from caldesmon, α-actinin, and several other actin-binding proteins. Thus, we consider that the 160kDa protein is a novel actin-binding protein.