title: Active site control of myosin cross-bridge zeta potential.
abstract: The electrical properties of contractile proteins contribute to muscle structure and perhaps function but have not been characterized adequately. Electrophoretic mobility, mu(e), is sensitive to the net electric charge and hydrodynamic size of a molecule in solution. Zeta potential, zeta, particle charge, Q(e), and particle charge-to-mass ratio are proportional to mu(e). We measured mu(e) for nucleotide complexes of skeletal muscle heavy meromyosin (HMM) and subfragment 1 (S1). The results indicate that mu(e) for HMM changes depending on the ligand bound in the active site. The changes in electric charge appear to occur mainly on the S1 moieties. For HMM(MgATPgammaS)(2) and HMM(MgADP.P(i))(2) the values of mu(e) are -0.077 and -0.17 (microm/s)/(V/cm), respectively. For these complexes, mu(e) is independent of [ATP], [ADP], and [P(i)]. When P(i) dissociates from HMM(MgADP.P(i))(2) to form HMM(MgADP)(2), mu(e) decreases to -0.61 (microm/s)/(V/cm). This large decrease in mu(e) is independent of free [ADP] or [ATP]. Increasing [P(i)], on the other hand, increases mu(e) for HMM(MgADP)(2) to values near those observed for the steady-state intermediate. For HMM, mu(e) = -0.34 and is independent of P(i). MgADP binding to HMM decreases mu(e) to -0.57 (microm/s)/(V/cm), and the dissociation constant is 9 microM. Taken together, these data indicate that mu(e) and, thus, zeta are controlled by ligand binding to the active site. The magnitudes of the particle charge-to-mass ratios for the HMM complexes are all in a range that falls within published values determined for a variety of other proteins. Possible roles that the observed nucleotide-dependent changes in cross-bridge electric charge might have in the contractile cycle in muscle are considered.
authors.affiliation: Department of Biochemistry, University of the Pacific School of Dentistry, San Francisco, California 94115-2399, USA.
authors.forename: William
authors.initials: W
authors.lastname: Bernt
authors.forename: Katherine
authors.initials: K
authors.lastname: Polosukhina
authors.forename: Bruce
authors.initials: B
authors.lastname: Weiner
authors.forename: Walther
authors.initials: W
authors.lastname: Tscharnuter
authors.forename: Stefan
authors.initials: S
authors.lastname: Highsmith
mesh_terms: D000244:Adenosine Diphosphate / Q000737:chemistry; D000255:Adenosine Triphosphate / Q000737:chemistry; D000818:Animals; D001665:Binding Sites; D004586:Electrophoresis; D046911:Macromolecular Substances; D018482:Muscle, Skeletal / Q000737:chemistry; D015879:Myosin Subfragments / Q000737:chemistry; D009218:Myosins / Q000737:chemistry*; D010316:Particle Size; D010710:Phosphates / Q000737:chemistry; D011817:Rabbits; D012996:Solutions; D055672:Static Electricity
chemical_list: D046911:Macromolecular Substances; D015879:Myosin Subfragments; D010710:Phosphates; D012996:Solutions; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D009218:Myosins