期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2004
卷号：101
期号：30
页码：10973-10978
DOI：10.1073/pnas.0401699101
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Current evidence favors the theory that, when the globular motor domain of myosin attaches to actin, the light chain binding domain or "lever arm" rotates, and thereby generates movement of actin filaments. Myosin is uniquely designed for such a role in that a long {alpha}-helix ({approx}9 nm) extending from the C terminus of the catalytic core is stabilized by two calmodulin-like molecules, the regulatory light chain (RLC) and the essential light chain (ELC). Here, we introduce a single-point mutation into the skeletal myosin RLC, which results in a large ({approx}50%) reduction in actin filament velocity (Vactin) without any loss in actin-activated MgATPase activity. Single-molecule analysis of myosin by optical trapping showed a comparable 2-fold reduction in unitary displacement or step size (d), without a significant change in the duration of the strongly attached state ({tau}on) after the power stroke. Assuming that Vactin {approx} d/{tau}on, we can account for the change in velocity primarily by a change in the step size of the lever arm without incurring any change in the kinetic properties of the mutant myosin. These results suggest that a principal role for the many light chain isoforms in the myosin II class may be to modulate the flexural rigidity of the light chain binding domain to maximize tension development and movement during muscle contraction.
