Myosin I from mammalian smooth muscle is regulated by caldesmon-calmodulin.
A single-headed monomeric myosin (myosin I) was isolated from pig urinary bladder smooth muscles and purified to homogeneity. Myosin I from smooth muscle is composed of a 110-kDa heavy chain and three 17-kDa light chains. The heavy chain from smooth muscle myosin I does not cross-react with the antibody against conventional myosin (myosin II) from smooth muscle, but it does show antigenic similarity to adrenal medulla myosin I heavy chain. The light chain from smooth muscle myosin I is similar to calmodulin in molecular weight, amino acid composition, and migration on SDS-polyacrylamide gel electrophoresis in the presence of Ca2+. The high salt ATPase activity of myosin I in the presence of CaCl2 is higher than that in K(+)-EDTA. Smooth muscle actin causes a 5-10-fold activation of the Mg-ATPase activity of myosin I. In the presence of Ca2+, exogenous calmodulin enhances the actin-activated ATPase activity of myosin I, and the increased activity is associated with the binding of exogenous calmodulin to myosin I heavy chain. A maximum of 4 mol of light chains/mol of myosin I heavy chain is observed in the presence of exogenous calmodulin. Caldesmon, a calmodulin/actin-binding protein, inhibits the actin-activated ATPase activity of myosin I. This inhibition is reversed by exogenous calmodulin in the presence of Ca2+. The actin activation of myosin I ATPase exhibits around 50% Ca2+ sensitivity in the presence of exogenous calmodulin. When caldesmon is bound to actin, Ca2+ sensitivity is increased to 80% in the presence of calmodulin. Therefore, smooth muscle caldesmon, which is thought to play a role in the regulation of actin activation of myosin II, also regulates the actin activation of myosin I ATPase in smooth muscle.
Chacko
S
S
Department of Pathobiology, University of Pennsylvania, Philadelphia 19104.
Jacob
S S
SS
Horiuchi
K Y
KY
D000199:Actins / Q000378:metabolism; D000313:Adrenal Medulla / Q000378:metabolism; D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase / Q000302:isolation & purification / Q000378:metabolism*; D002118:Calcium / Q000494:pharmacology; D002147:Calmodulin / Q000378:metabolism*; D002148:Calmodulin-Binding Proteins / Q000378:metabolism*; D002850:Chromatography, Gel; D002852:Chromatography, Ion Exchange; D003429:Cross Reactions; D004591:Electrophoresis, Polyacrylamide Gel; D007700:Kinetics; D046911:Macromolecular Substances; D008970:Molecular Weight; D009130:Muscle, Smooth / Q000378:metabolism*; D009218:Myosins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D013552:Swine; D001743:Urinary Bladder / Q000378:metabolism*
D000199:Actins; D002147:Calmodulin; D002148:Calmodulin-Binding Proteins; D046911:Macromolecular Substances; D017301:Ca(2+) Mg(2+)-ATPase; D009218:Myosins; D002118:Calcium