Electrostatic changes at the actomyosin-subfragment 1 interface during force-generating reactions.
The ionic strength dependence of the binding of rabbit skeletal muscle myosin subfragment 1, S1, to F-actin in the presence of saturating concentrations of MgATP or MgADP was analyzed in order to determine the association constants at zero ionic strength [K(0)] and the products of the net effective electric charges (magnitude of zMzA) at the binding interfaces. K(0) and magnitude of zM A were 1 x 10(6) M-1 and 17 esu2 for S1-MgADP,P, and 5 x 10(7) M-1 and 7 esu2 for S1-MgADP, respectively, for binding to F-actin at 25 degrees C. At ionic strengths near physiological, the increase in affinity is close to 10(4)-fold for this transition that may correspond to force generation in muscle fibers. The large, from 17 to 7 esu2, decrease in the electrostatic contribution to binding appears to be correlated with a much larger increase in nonelectrostatic interactions, unlike the simpler transition of actin-bound S1-MgADP to S1, which appears to be due entirely to electrostatic changes [Highsmith, S. (1990) Biochemistry 29, 10690-10694]. These results for acto-S1-MgADP,P to acto-S1-MgADP suggest that a substantial transformation of the actin binding site on S1 occurs even if there is a translocation to a new interface.
Highsmith
S
S
Department of Biochemistry, School of Dentistry, University of the Pacific, San Francisco, California 94115.
Murphy
A J
AJ
D000199:Actins / Q000378:metabolism; D000205:Actomyosin / Q000737:chemistry / Q000378:metabolism*; D000244:Adenosine Diphosphate / Q000378:metabolism; D000818:Animals; D004563:Electrochemistry; D007700:Kinetics; D009119:Muscle Contraction; D015879:Myosin Subfragments / Q000737:chemistry / Q000378:metabolism*; D009994:Osmolar Concentration; D011485:Protein Binding; D011817:Rabbits; D014961:X-Ray Diffraction
D000199:Actins; D015879:Myosin Subfragments; D000244:Adenosine Diphosphate; D000205:Actomyosin