Kimura S, Ichikawa A, Ishizuka J, Ohkouchi S, Kake T, Maruyama K
Department of Biology, Faculty of Science, Chiba University, Japan.
Eur J Biochem. 1999 Jul;263(2):396-401. doi: 10.1046/j.1432-1327.1999.00505.x.
Tropomodulin is a tropomyosin-binding protein, originally isolated from human erythrocytes. Tropomodulin is currently regarded as the sole actin pointed-end capping protein [Weber, A., Pennise, C.R., Babcock, G.G. & Fowler, V.M. (1994) J. Cell Biol. 127, 1627-1635]. This work first describes a procedure for the purification of tropomodulin from rabbit skeletal muscle. Tropomodulin almost completely inhibited filament formation of actin in the presence of tropomyosin and troponin. For the maximal inhibition of actin polymerization, approximately 0.10, 0.12 and 0.003 mol of tropomyosin, troponin and tropomodulin per mol of actin were required, respectively. Fluorescence-intensity measurements, electron-microscopy and sedimentation experiments revealed that only very short fragments and amorphous aggregates, but not filaments, were formed when actin was copolymerized with tropomyosin, troponin and tropomodulin by the addition of 50 mM KCl at pH 8.0. The effects of tropomyosin, troponin and tropomodulin were more remarkable on Ca-actin than on Mg-actin. It appears that tropomodulin caps both the pointed and barbed ends of tropomyosin- and troponin-bound actin filaments.
原肌球蛋白调节蛋白是一种与原肌球蛋白结合的蛋白质，最初从人红细胞中分离得到。目前，原肌球蛋白调节蛋白被认为是唯一的肌动蛋白尖端封端蛋白[韦伯，A.，彭尼斯，C.R.，巴布科克，G.G. & 福勒，V.M.（1994年）《细胞生物学杂志》127卷，第1627 - 1635页]。这项工作首次描述了从兔骨骼肌中纯化原肌球蛋白调节蛋白的方法。在原肌球蛋白和肌钙蛋白存在的情况下，原肌球蛋白调节蛋白几乎完全抑制了肌动蛋白丝的形成。为了最大程度地抑制肌动蛋白聚合，每摩尔肌动蛋白分别需要约0.10、0.12和0.003摩尔的原肌球蛋白、肌钙蛋白和原肌球蛋白调节蛋白。荧光强度测量、电子显微镜和沉降实验表明，当在pH 8.0条件下加入50 mM氯化钾使肌动蛋白与原肌球蛋白、肌钙蛋白和原肌球蛋白调节蛋白共聚时，仅形成非常短的片段和无定形聚集体，而没有形成丝。原肌球蛋白、肌钙蛋白和原肌球蛋白调节蛋白对钙 - 肌动蛋白的作用比对镁 - 肌动蛋白的作用更显著。似乎原肌球蛋白调节蛋白封端了与原肌球蛋白和肌钙蛋白结合的肌动蛋白丝的尖端和倒刺端。
