Pruliere G, Fuller S D, Weeds A G, d'Albis A, der Terrossian E
J Mol Biol. 1986 Dec 20;192(4):815-30. doi: 10.1016/0022-2836(86)90031-8.
Pig platelet tropomyosin exhibits many of the functional activities of skeletal tropomyosin. At low ionic strength it forms end-to-end aggregates similar to those formed by skeletal tropomyosins. It forms a 1:1 complex with muscle troponin or with a troponin I-pig brain calmodulin complex, as well as a 1:6 association with platelet filamentous actin. Electron microscopy of paracrystals shows that the troponin binding site is slightly C-terminal of the unique cysteine, corresponding to position 190 of the rabbit skeletal alpha-tropomyosin sequence. The effect of a complex comprising platelet actin and tropomyosin on the ATPase activity of rabbit skeletal muscle myosin subfragment-1 was similar to that displayed by its skeletal muscle counterpart. Platelet tropomyosin decreased the activity by roughly half in a calcium-independent manner. Addition of troponin to the actin-tropomyosin in the absence of calcium results in further inhibition and allows the full activity of the complex to be restored by Ca2+. These results differ from those obtained by Côté & Smillie for horse platelet tropomyosin and this may reflect the different isomeric nature of pig platelet tropomyosin. These results suggest that the functional properties of non-muscle tropomyosins may differ when comparisons are made between proteins isolated from the same type of cell but in different species. Differences in self-association and actin-binding properties may be finely graded between different isoforms.
猪血小板原肌球蛋白展现出许多骨骼肌原肌球蛋白的功能活性。在低离子强度下，它会形成类似于骨骼肌原肌球蛋白形成的端对端聚集体。它与肌肉肌钙蛋白或肌钙蛋白I - 猪脑钙调蛋白复合物形成1:1复合物，以及与血小板丝状肌动蛋白形成1:6缔合。平行晶体的电子显微镜观察表明，肌钙蛋白结合位点位于独特半胱氨酸的略微C端，对应于兔骨骼肌α-原肌球蛋白序列的第190位。包含血小板肌动蛋白和原肌球蛋白的复合物对兔骨骼肌肌球蛋白亚片段-1的ATP酶活性的影响与其骨骼肌对应物所显示的相似。血小板原肌球蛋白以不依赖钙的方式将活性降低约一半。在没有钙的情况下向肌动蛋白 - 原肌球蛋白中添加肌钙蛋白会导致进一步抑制，并使复合物的全部活性通过Ca2 +恢复。这些结果与Côté和Smillie对马血小板原肌球蛋白获得的结果不同，这可能反映了猪血小板原肌球蛋白不同的异构体性质。这些结果表明，当比较从同一类型细胞但不同物种中分离的蛋白质时，非肌肉原肌球蛋白的功能特性可能不同。不同同工型之间自我缔合和肌动蛋白结合特性的差异可能是细微分级的。
