Calcium- and Actin-Binding Sites in F-Actin Crosslinking Molecules from Dictyostelium Discoideum

Abstract

Numerous actin-binding proteins regulate the viscosity and elasticity of the cytoplasm by either interfering directly with the equilibrium of G- and F-actin, or by crosslinking the filaments (for reviews see Stossel et al.(1985; Pollard and Cooper, 1986). F-actin crosslinking proteins are usually dimers that form a three dimensional network via two binding sites for actin. The most prominent F-actin crosslinking activities in Dictyostelium discoideum are due to two proteins with apparent molecular weights of 95.000 (K-actinin)(Condeelis and Vahey, 1982; Fechheimer et al.(1982) and 120.000 (gelation factor) (Condeelis et al.f 1982). Cloning and sequencing of the genes coding for these cytoskeletal proteins revealed similarities to proteins from other species including mammals. These similarities may help to identify functional domains that are involved in the binding to actin and in the regulation by calcium ions.