Mak A S, Smillie L B, Stewart G R
J Biol Chem. 1980 Apr 25;255(8):3647-55.
Elucidation of the complete amino acid sequence of rabbit skeletal beta-tropomyosin has shown that it has the same number of residues (284) per chain as the alpha component from the same source. The presence of more than one form of beta-tropomyosin was indicated by the detection of heterogeneity at 11 positions in the sequence. The ratio of the major form to the minor form(s) was estimated to be about 10:1. Of the 39 amino acid residue differences in the major alpha and beta forms, most involve chemically similar residues with only two leading to a more negative net charge on the beta form (Ser-229 to glutamic acid and His-276 to asparagine). These replacements do not significantly affect the repeating heptapeptide pattern of nonpolar and polar residues in tropomyosin nor the 14-fold periodicity of acidic and outer nonpolar residues implicated in its binding to F-actin. The larger number of substitutions in the COOH-terminal half of the protein is reflected in differences in the smoothed alpha-helix parameters of the beta-tropomyosin sequence when compared with that of the alpha component. These differences may be related to a lower binding affinity of beta-tropomyosin to troponin.
对兔骨骼肌β-原肌球蛋白完整氨基酸序列的解析表明，其每条链的残基数量（284个）与来自同一来源的α组分相同。序列中11个位置存在异质性，这表明存在不止一种形式的β-原肌球蛋白。主要形式与次要形式的比例估计约为10:1。在主要的α和β形式中存在39个氨基酸残基差异，其中大多数涉及化学性质相似的残基，只有两个差异导致β形式的净电荷更负（Ser-229替换为谷氨酸，His-276替换为天冬酰胺）。这些替换不会显著影响原肌球蛋白中非极性和极性残基的重复七肽模式，也不会影响其与F-肌动蛋白结合所涉及的酸性和外部非极性残基的14倍周期性。与α组分相比，蛋白质COOH末端一半中更多的替换反映在β-原肌球蛋白序列的平滑α-螺旋参数差异上。这些差异可能与β-原肌球蛋白与肌钙蛋白的较低结合亲和力有关。
