Site-specific inhibition of myosin-mediated motility in vitro by monoclonal antibodies.

Abstract

Monoclonal antibodies directed against 7 different sites on Dictyostelium myosin were tested for their ability to inhibit movement of myosin in vitro, using the Nitella-based myosin-mediated bead movement assay. To complement this functional assay, the binding sites of these antibodies were located by EM, using the rotary shadowing technique. One antibody bound to the 18,000-dalton light chain and inhibited movement completely. All of the remaining antibodies bound to various positions along the rod portion of the myosin molecule, which is .apprx. 1800 .ANG. long. Antibodies that bound to the rod .apprx. 470, 680 and 1400 .ANG. from the head-tail junction did not alter myosin movement. One antibody appeared to bind very close to the head-tail junction and to inhibit movement 50%. Surprisingly, 3 antibodies that bound .apprx. 1200 .ANG. from the head-tail junction inhibited movement completely. This inhibition did not depend on using intact IgG, since Fab'' fragments had the same effect.