Highsmith S, Eden D
Department of Biochemistry, School of Dentistry, University of the Pacific, San Francisco, California 94115.
Biochemistry. 1993 Mar 16;32(10):2455-8. doi: 10.1021/bi00061a001.
The hydrodynamic size of rabbit skeletal muscle myosin subfragment 1 (S1) is decreased when S1 and MgATP form the steady-state intermediate S1-MgADP,P(i). The rotational decay time, tau, determined by transient electrical birefringence techniques was 259 ns for S1-MgADP,P(i) and 271 ns for S1-MgADP at 3 degrees C in low ionic strength solutions. The data were interpreted using a hydrodynamic model consisting of a rigid linear four-bead structure that had a point at the center of one of the inner beads about which the structure can bend. The structure of S1-MgADP was approximated by adjusting the bend angle to 20 degrees. The best fit to the S1-MgADP,P(i) decay time was then obtained when the angle was increased to 38 degrees. The results obtained using this simple model suggest that MgATP binding and hydrolysis changes the structure of S1 so that one end of it moves by at least 3.9 nm. The reverse of this process, during product release, would provide a displacement large enough to account for most of the ATP-driven filament sliding that occurs in muscle or in in vitro motility assays.
当兔骨骼肌肌球蛋白亚片段1（S1）与MgATP形成稳态中间体S1-MgADP，P（i）时，其流体动力学尺寸会减小。在低离子强度溶液中，于3℃下，通过瞬态电双折射技术测定的S1-MgADP，P（i）的旋转衰减时间τ为259 ns，S1-MgADP的旋转衰减时间τ为271 ns。使用由刚性线性四珠结构组成的流体动力学模型对数据进行解释，该结构在其中一个内珠的中心有一个点，结构可围绕该点弯曲。通过将弯曲角度调整为20°来近似S1-MgADP的结构。当角度增加到38°时，可得到与S1-MgADP，P（i）衰减时间的最佳拟合。使用这个简单模型获得的结果表明，MgATP的结合和水解会改变S1的结构，使其一端移动至少3.9 nm。在产物释放过程中，这一过程的逆转将提供足够大的位移，以解释肌肉中或体外运动测定中发生的大部分由ATP驱动的细丝滑动。
