title: Stimulation of the interaction between actin and myosin by Physarum caldesmon-like protein and smooth muscle caldesmon.
abstract: We have purified an actin-binding protein from the plasmodia of a lower eukaryote, Physarum polycephalum, with an apparent molecular mass of 210,000 daltons on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. This protein bound to actin filaments with a stoichiometry of 1:7-8 in a Ca(2+)-calmodulin-dependent manner. Antibody raised against caldesmon from smooth muscle cross-reacted with the 210-kDa protein. In vitro motility assay revealed that the 210-kDa protein increased the sliding velocity of actin filaments on Physarum myosin. The 210-kDa protein more than doubled the actin-activated ATPase activity of Physarum myosin under comparative conditions of in vitro motility assay. Further increases in the concentration of the 210-kDa protein decreased its stimulatory effects. Ca(2+)-calmodulin prevented the stimulatory effects of the 210-kDa protein. Unexpectedly, smooth muscle caldesmon also increased the sliding velocity of actin filaments on smooth muscle myosin at lower concentrations. The well-known inhibitory effect of smooth muscle caldesmon on the actin-myosin interaction was observed with this motility assay when the concentration of the caldesmon was increased further. The stimulatory and inhibitory effects were confirmed by measurements of actin-activated ATPase activity of smooth muscle myosin. From estimations of the intracellular concentrations of the 210-kDa protein and smooth muscle caldesmon in vivo, it appears that effects of the former and the latter on actin-myosin interactions in vivo are stimulatory and inhibitory, respectively.
authors.affiliation: Department of Pharmacology, Gunma University School of Medicine, Japan.
authors.forename: R
authors.initials: R
authors.lastname: Ishikawa
authors.forename: T
authors.initials: T
authors.lastname: Okagaki
authors.forename: S
authors.initials: S
authors.lastname: Higashi-Fujime
authors.forename: K
authors.initials: K
authors.lastname: Kohama
mesh_terms: D000199:Actins / Q000378:metabolism*; D000818:Animals; D002148:Calmodulin-Binding Proteins / Q000302:isolation & purification / Q000378:metabolism*; D002645:Chickens; D003429:Cross Reactions; D004533:Egtazic Acid / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D005656:Fungal Proteins / Q000302:isolation & purification / Q000378:metabolism*; D005895:Gizzard, Avian / Q000378:metabolism; D007700:Kinetics; D008954:Models, Biological; D008970:Molecular Weight; D009130:Muscle, Smooth / Q000378:metabolism*; D009218:Myosins / Q000378:metabolism*; D016839:Physarum polycephalum / Q000378:metabolism*
chemical_list: D000199:Actins; D002148:Calmodulin-Binding Proteins; D005656:Fungal Proteins; D004533:Egtazic Acid; D009218:Myosins