Hopkins Seth C, Sabido-David Cibele, van der Heide Uulke A, Ferguson Roisean E, Brandmeier Birgit D, Dale Robert E, Kendrick-Jones John, Corrie John E T, Trentham David R, Irving Malcolm, Goldman Yale E
Pennsylvania Muscle Institute, University of Pennsylvania, Philadelphia 19104-6083, USA.
J Mol Biol. 2002 May 17;318(5):1275-91. doi: 10.1016/s0022-2836(02)00189-4.
Structural changes in myosin power many types of cell motility including muscle contraction. Tilting of the myosin light chain domain (LCD) seems to be the final step in transducing the energy of ATP hydrolysis, amplifying small structural changes near the ATP binding site into nanometer-scale motions of the filaments. Here we used polarized fluorescence measurements from bifunctional rhodamine probes attached at known orientations in the LCD to describe the distribution of orientations of the LCD in active contraction and rigor. We applied rapid length steps to perturb the orientations of the population of myosin heads that are attached to actin, and thereby characterized the motions of these force-bearing myosin heads. During active contraction, this population is a small fraction of the total. When the filaments slide in the shortening direction in active contraction, the long axis of LCD tilts towards its nucleotide-free orientation with no significant twisting around this axis. In contrast, filament sliding in rigor produces coordinated tilting and twisting motions.
肌球蛋白的结构变化推动了包括肌肉收缩在内的多种细胞运动类型。肌球蛋白轻链结构域（LCD）的倾斜似乎是转换ATP水解能量的最后一步，将ATP结合位点附近的微小结构变化放大为细丝的纳米级运动。在这里，我们使用附着在LCD中已知方向的双功能罗丹明探针进行偏振荧光测量，以描述LCD在主动收缩和僵直状态下的方向分布。我们应用快速长度步进来扰动附着在肌动蛋白上的肌球蛋白头部群体的方向，从而表征这些承载力的肌球蛋白头部的运动。在主动收缩过程中，这个群体只占总数的一小部分。当细丝在主动收缩中沿缩短方向滑动时，LCD的长轴朝着其无核苷酸方向倾斜，且围绕该轴没有明显的扭转。相比之下，在僵直状态下细丝滑动会产生协调的倾斜和扭转运动。
