title: Changes in Mg2+ ion concentration and heavy chain phosphorylation regulate the motor activity of a class I myosin.
abstract: Class I myosins are single-headed motor proteins implicated in various motile processes including organelle translocation, ion channel gating, and cytoskeleton reorganization. Dictyostelium discoideum myosin-ID belongs to subclass 1alpha, whose members are thought to be tuned for rapid sliding. The direct analysis of myosin-ID motor activity is made possible by the production of single polypeptide constructs carrying an artificial lever arm. Using these constructs, we show that the motor activity of myosin-ID is activated 80-fold by phosphorylation at the TEDS site. TEDS site phosphorylation acts by stabilizing the actomyosin complex and increasing the coupling between actin binding and the release of hydrolysis products. A surprising effect of Mg(2+) ions on in vitro motility was discovered. Changes in the level of free Mg(2+) ions within the physiological range are shown to modulate motor activity by inhibiting ADP release. Our results indicate that higher concentrations of free Mg(2+) ions stabilize the tension-bearing actin myosin ADP state and shift the system from the production of rapid movement toward the generation of tension.
authors.affiliation: Department of Biophysics, Max-Planck-Institute for Medical Research, Jahnstrasse 29, D-69120 Heidelberg, Germany.
authors.forename: Setsuko
authors.initials: S
authors.lastname: Fujita-Becker
authors.forename: Ulrike
authors.initials: U
authors.lastname: Dürrwang
authors.forename: Muriel
authors.initials: M
authors.lastname: Erent
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Clark
authors.forename: Michael A
authors.initials: MA
authors.lastname: Geeves
authors.forename: Dietmar J
authors.initials: DJ
authors.lastname: Manstein
mesh_terms: D000199:Actins / Q000378:metabolism; D000205:Actomyosin / Q000378:metabolism; D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D002413:Cations, Divalent / Q000378:metabolism*; D004023:Dictyostelium; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism* / Q000494:pharmacology; D020409:Molecular Motor Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D009068:Movement / Q000187:drug effects; D009154:Mutation / Q000235:genetics; D018995:Myosin Heavy Chains / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D024461:Myosin Type I / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D011485:Protein Binding; D013816:Thermodynamics; D017186:Titrimetry
chemical_list: D000199:Actins; D002413:Cations, Divalent; D020409:Molecular Motor Proteins; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D000205:Actomyosin; D024461:Myosin Type I; D018995:Myosin Heavy Chains; D008274:Magnesium