Hannon J D, Chase P B, Martyn D A, Huntsman L L, Kushmerick M J, Gordon A M
Department of Physiology and Biophysics, University of Washington, Seattle 98195.
Biophys J. 1993 May;64(5):1632-7. doi: 10.1016/S0006-3495(93)81517-0.
A conformational change accompanying Ca2+ binding to troponin C (TnC) constitutes the initial event in contractile regulation of vertebrate striated muscle. We replaced endogenous TnC in single skinned fibers from rabbit psoas muscle with a modified form of cardiac TnC (cTnC) which, unlike native cTnC, probably contains an intramolecular disulfide bond. We found that such activating TnC (aTnC) enables force generation and shortening in the absence of calcium. With aTnC, both force and shortening velocity were the same at pCa 9.2 and pCa 4.0. aTnc could not be extracted under conditions which resulted in extraction of endogenous TnC. Thus, aTnC provides a stable model for structural studies of a calcium binding protein in the active conformation as well as a useful tool for physiological studies on the primary and secondary effects of Ca2+ on the molecular kinetics of muscle contraction.
伴随着钙离子与肌钙蛋白C（TnC）结合的构象变化是脊椎动物横纹肌收缩调节的初始事件。我们用一种修饰形式的心脏肌钙蛋白C（cTnC）替代了来自兔腰大肌的单根去皮纤维中的内源性TnC，这种修饰后的cTnC与天然cTnC不同，可能含有分子内二硫键。我们发现，这种激活型TnC（aTnC）能够在没有钙离子的情况下产生力并实现缩短。使用aTnC时，在pCa 9.2和pCa 4.0条件下，力和缩短速度是相同的。在导致内源性TnC被提取的条件下，aTnC无法被提取。因此，aTnC为处于活性构象的钙结合蛋白的结构研究提供了一个稳定的模型，同时也是研究钙离子对肌肉收缩分子动力学的一级和二级效应的生理学研究的有用工具。
