Abstract
We have reported that myosin XI purified from tobacco cultured BY-2 cells can walk processively on an actin filament with 35nm steps (EMBO J. 2003 vol. 22 pp. 1263-1272). In the present study, we studied the mechanism of inhibitory regulation by Ca2+. When myosin was treated with Ca2+ at concentrations higher than pCa5.5, light chain (calmodulin) detached and affinity between myosin and actin filament decreased. Ca2+ did not affect the actin activated ATPase. In in vitro motility assay, sliding movement of actin filament was observed even in the presence of Ca2+, when myosin density was increased. We estimated the elasticity of myosin molecule by measuring the rotation of short actin filament attached to a single myosin molecule in the absence of ATP. Ca2+ treatment decreased the Brownian movement of actin filament, indicating that the long neck of myosin folded and became shorter and rigid by removal of calmodulin.
