Lehrer S S, Golitsina N L, Geeves M A
Muscle Research Laboratories, Boston Biomedical Research Institute, Massachusetts 02114.
Biochemistry. 1997 Nov 4;36(44):13449-54. doi: 10.1021/bi971568w.
Tropomyosin (Tm) bound to actin induces cooperative activation of actomyosin subfragment 1 (actin-S1) ATPase, observed as a sigmoid ATPase vs [S1] dependence. The activation is much steeper for gizzard muscle Tm (GTm) than for rabbit skeletal Tm (RSTm). To investigate if this greater cooperativity is due to increased communication between GTms along the thin filament, we studied effects of S1 binding on the state of actin-Tm using the fluorescence of pyrene-labeled Tm. Kinetic and equilibrium studies provided values for n, the apparent cooperative unit size [Geeves, M. A., and Lehrer, S. S. (1994) Biophys. J. 67, 273]. We report comparative studies of Tm-actin-S1 ATPase with values of n using GTm, RSTm, and 5aTm, a 1/7 shorter nonmuscle Tm from rat fibroblast cells [Pittenger, M. F., et al. (1994) Curr. Opin. Cell Biol., 6, 96]. 5aTm and GTm produce similar cooperative activation of actin-S1 ATPase and have similar n values that are 2-fold greater than RSTm, indicating a correlation between ATPase activation and n value. This appears to be due to the similarity of the C-terminal amino acid sequences of 5a and GTm which produce strong end-to-end interactions. The results are discussed in terms of a continuous flexible Tm strand on the actin filament.
与肌动蛋白结合的原肌球蛋白（Tm）会诱导肌动球蛋白亚片段1（肌动蛋白-S1）ATP酶的协同激活，这表现为ATP酶活性与[S1]之间呈S形依赖关系。砂囊肌Tm（GTm）的激活比兔骨骼肌Tm（RSTm）更为陡峭。为了研究这种更强的协同性是否是由于GTm沿细肌丝之间的通讯增加所致，我们利用芘标记的Tm的荧光研究了S1结合对肌动蛋白-Tm状态的影响。动力学和平衡研究提供了表观协同单位大小n的值[吉夫斯，M. A.，和莱勒，S. S.（1994年）《生物物理学杂志》67卷，273页]。我们报告了对Tm-肌动蛋白-S1 ATP酶的比较研究，给出了使用GTm、RSTm和5aTm时的n值，5aTm是大鼠成纤维细胞中一种短1/7的非肌肉Tm[皮滕杰，M. F.等人（1994年）《细胞生物学当前观点》6卷，96页]。5aTm和GTm对肌动蛋白-S1 ATP酶产生相似的协同激活，且具有相似的n值，该值比RSTm大2倍，表明ATP酶激活与n值之间存在相关性。这似乎是由于5aTm和GTm的C末端氨基酸序列相似，它们之间会产生强烈的端对端相互作用。我们根据肌动蛋白丝上连续的柔性Tm链对结果进行了讨论。
