Phenylglyoxal Reveals Phosphorylation-Dependent Difference in the Conformation of Acanthamoeba Myosin II Active Site

Acanthamoeba myosin II is regulated in an unique way by phosphorylation of three serine residues located within nonhelical tailpiece of the rod domain. Phosphorylation inhibits functions associated with the NH2-terminal motor domain, i.e., actin-activated activity and ability to move actin filaments. Number of data indicate functional communication between these distant domains. In this work, effect of modification of arginine residues with phenylglyoxal on the Ca2+-ATPase activity and susceptibility to endoproteinase ArgC cleavage of monomeric phospho- and dephosphomyosin II has been investigated. Upon the phenylglyoxal treatment the activity of dephosphomyosin II was decreasing faster that the activity of phosphomyosin. The modification also affected the proteolytic fragmentation of phospho- and dephosphomyosin II: the cleavage of heavy chain was further inhibited for phosphomyosin and enhanced for dephosphomyosin with a concomitant exposure of an additional cleavage site within the head domain. No difference in the quantity of modified arginines was observed. These results indicate a difference between the conformation of active sites of phospho- and dephosphomyosin II.