title: Limited proteolysis reveals a structural difference in the globular head domains of dephosphorylated and phosphorylated Acanthamoeba myosin II.
abstract: Phosphorylation at three sites at the tip of the tail of myosin II from Acanthamoeba castellanii inactivates the actin-activated Mg(2+)-ATPase activity of filamentous myosin and the in vitro motility activity of both monomeric and filamentous myosin. To seek a structural explanation for these effects, we examined the susceptibilities of dephosphorylated and phosphorylated myosins II to endoproteinases. Endoproteinase Arg-C cleaved myosin II preferentially at two sites in the globular head, Lys-621 and Arg-638, producing an NH2-terminal fragment of about 67,000 Da and a COOH-terminal fragment of about 112,000 Da. Dephosphorylated monomers and filaments were cleaved about 3 times more rapidly than their phosphorylated counterparts principally because of a much greater rate of cleavage at Arg-638; the ratio of cleavage at Arg-638:Lys-621 was about 3 for dephosphorylated myosins and about 0.5 for phosphorylated myosins. These data demonstrate that phosphorylation at the tip of the tail of Acanthamoeba myosin II causes a conformational change in the globular head that contains the catalytic sites; therefore, this conformational change may be related to the different catalytic and motile activities of the dephosphorylated and phosphorylated enzymes.
authors.affiliation: Laboratory of Cell Biology, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892.
authors.forename: C
authors.initials: C
authors.lastname: Ganguly
authors.forename: B
authors.initials: B
authors.lastname: Martin
authors.forename: M
authors.initials: M
authors.lastname: Bubb
authors.forename: E D
authors.initials: ED
authors.lastname: Korn
mesh_terms: D000048:Acanthamoeba / Q000201:enzymology*; D000595:Amino Acid Sequence; D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism*; D010450:Endopeptidases; D007700:Kinetics; D008969:Molecular Sequence Data; D009218:Myosins / Q000378:metabolism*; D010446:Peptide Fragments / Q000302:isolation & purification; D010449:Peptide Mapping; D010766:Phosphorylation
chemical_list: D010446:Peptide Fragments; D010450:Endopeptidases; D017301:Ca(2+) Mg(2+)-ATPase; D009218:Myosins