EFFECTS OF PHOSPHORYLATION AND NUCLEOTIDES ON THE CONFORMATION OF MYOSIN-II FROM ACANTHAMOEBA-CASTELLANII

The actin-activated Mg2+-ATPase activity of filamentous Acanthamoeba m yosin II is inactivated by phosphorylation of a short non-helical tail piece at the C-terminal end of each heavy chain even though the cataly tic sites are in the N-terminal globular head. Consistent with this ef fect, phosphorylation at the tip of the tail alters the conformation o f the head as shown by a shift in the principal site of cleavage by en doproteinase Arg-C (Ganguly, C., Martin, B., Bubb, M., and Kern, E. D. (1992) J. Biol. Chem. 267, 20905-20908). We now show that the sedimen tation coefficient of monomeric phospho-myosin II is 1.3-4.6% lower th an that of dephospho-myosin II, which suggests that phosphorylation pr oduces a less compact conformation with a small increase in frictional coefficient. As shown by changes in papain digestion patterns, bound nucleotide also affects the conformation of the head region of monomer ic phospho- and dephospho-myosin II, the conformation of the head regi on of filamentous phospho- and dephospho-myosin II, and the conformati on of the C-terminal region of the tail of filamentous phospho-myosin II, Conformational differences between the dephospho- and phospho-form s of myosin II in the presence of nucleotide, as detected by susceptib ility to proteolysis, therefore, appear to be greater in filaments tha n in monomers. These results provide additional evidence for communica tion between the N-terminal heads and C-terminal tails of Acanthamoeba myosin II.