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：2014
卷号：111
期号：12
页码：4626-4631
DOI：10.1073/pnas.1321868111
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Time-resolved changes in the conformation of troponin in the thin filaments of skeletal muscle were followed during activation in situ by photolysis of caged calcium using bifunctional fluorescent probes in the regulatory and the coiled-coil (IT arm) domains of troponin. Three sequential steps in the activation mechanism were identified. The fastest step (1,100 s-1) matches the rate of Ca2+ binding to the regulatory domain but also dominates the motion of the IT arm. The second step (120 s-1) coincides with the azimuthal motion of tropomyosin around the thin filament. The third step (15 s-1) was shown by three independent approaches to track myosin head binding to the thin filament, but is absent in the regulatory head. The results lead to a four-state structural kinetic model that describes the molecular mechanism of muscle activation in the thin filament-myosin head complex under physiological conditions.
