title: Interaction of actin and ADP with the head domain of smooth muscle myosin: implications for strain-dependent ADP release in smooth muscle.
abstract: Transient kinetic methods were used to study interactions between actin, MgADP, and smooth muscle (chicken gizzard) myosin subfragment 1 (smS1). The equilibrium dissociation constant (Kd) of actin for smS1 was 3.5 nM, tighter than that of skeletal S1 (skS1). Actin binding to smS1 was weakened 5-fold by saturation with ADP compared to 30-60-fold for skS1. The Kd of ADP for smS1 was increased from 1.2 to 5 microM by actin, whereas for skS1 values increased from 2 to 100 microM. Thus, coupling between ADP and actin binding is weaker for smS1. Previous studies show that release of ADP from actin.smS1.ADP produces a tilt of the regulatory domain [Whittaker, M., Wilson-Kubalek, E. M., Smith, J. E., Faust, L., Milligan, R. A., and Sweeney, H. L. (1995) Nature 378, 748-751]. This result was confirmed by independent structural methods; tilting was absent for skS1, and the Kd for ADP was in agreement with the values measured here [Gollub, J., Cremo, C. R., and Cooke, R. (1996) Nat. Struct. Biol. 3, 796-802; Poole, K. I. V., Lorenz, M., Ellison, P., Evans, G., Rosenbaum, G., Boesecke, P., Holmes, K. C., and Cremo, C. R. (1997) J. Muscle Res. Cell Motility 18, 264]. We discuss tilting upon ADP release with respect to our measurements, previous measurements with skS1, and nucleotide concentrations in smooth muscle. We propose that these data suggest a strain-dependent ADP release mechanism that may be accentuated in smooth muscles.
authors.affiliation: Department of Biochemistry and Biophysics, Washington State University, Pullman 99164, USA. cremo@wsu.edu
authors.forename: C R
authors.initials: CR
authors.lastname: Cremo
authors.forename: M A
authors.initials: MA
authors.lastname: Geeves
mesh_terms: D000199:Actins / Q000378:metabolism*; D000244:Adenosine Diphosphate / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D002645:Chickens; D007700:Kinetics; D018482:Muscle, Skeletal / Q000378:metabolism; D009130:Muscle, Smooth / Q000378:metabolism*; D015879:Myosin Subfragments / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D011817:Rabbits; D013045:Species Specificity; D013050:Spectrometry, Fluorescence; D013816:Thermodynamics
chemical_list: D000199:Actins; D015879:Myosin Subfragments; D000244:Adenosine Diphosphate