Pearlstone J R, Smillie L B
J Biol Chem. 1983 Feb 25;258(4):2534-42.
The binding of troponin-I to tropomyosin, as well as its effects on the binding of troponin-T and its fragments T1 (residues 1-158) and T2 (residues 159-259) to tropomyosin, have been studied using immobilized alpha-tropomyosin. When applied alone, troponin-I exhibited weak interaction with tropomyosin and was eluted with a NaCl gradient at 0.12 M. Intact troponin-T was eluted at 0.40 M NaCl, while its fragment T1 was eluted from site 1 (near the COOH terminus of tropomyosin) at 0.32 M, independently from T2, which was eluted from site 2 (near Cys-190) at 0.22 M NaCl. However, the simultaneous presence of troponin-I and T2 resulted in formation of a strong troponin-I/T2/tropomyosin ternary complex at site 2 such that troponin-I/T2 complex was now eluted at 0.45 to 0.5 M NaCl. This binding was Ca2+-sensitive in the presence of troponin-C. An additional effect of troponin-I binding at site 2 was the strengthening of the T1/tropomyosin interaction at site 1, such that T1 was now eluted at the higher value of 0.45 to 0.50 M NaCl. Troponin-I also enhanced the binding of intact troponin-T to tropomyosin. These results suggest that cooperativity exists between the two sites, presumably induced by the binding of troponin-I to tropomyosin and mediated by a conformational change in the latter.
利用固定化的α-原肌球蛋白，研究了肌钙蛋白I与原肌球蛋白的结合，以及其对肌钙蛋白T及其片段T1（第1 - 158位氨基酸残基）和T2（第159 - 259位氨基酸残基）与原肌球蛋白结合的影响。单独应用时，肌钙蛋白I与原肌球蛋白表现出弱相互作用，并在0.12 M的NaCl梯度下被洗脱。完整的肌钙蛋白T在0.40 M NaCl时被洗脱，而其片段T1在0.32 M时从位点1（靠近原肌球蛋白的COOH末端）被洗脱，与T2无关，T2在0.22 M NaCl时从位点2（靠近Cys - 190）被洗脱。然而，肌钙蛋白I和T2同时存在时，在位点2形成了强的肌钙蛋白I/T2/原肌球蛋白三元复合物，使得肌钙蛋白I/T2复合物现在在0.45至0.5 M NaCl时被洗脱。在肌钙蛋白C存在的情况下，这种结合对Ca2 +敏感。肌钙蛋白I在位点2结合的另一个作用是加强了T1/原肌球蛋白在位点1的相互作用，使得T1现在在0.45至0.50 M NaCl的较高值时被洗脱。肌钙蛋白I还增强了完整肌钙蛋白T与原肌球蛋白的结合。这些结果表明，两个位点之间存在协同作用，推测是由肌钙蛋白I与原肌球蛋白的结合诱导，并由后者的构象变化介导。
