Wang C L, Zhan Q, Tao T, Gergely J
J Biol Chem. 1987 Jul 15;262(20):9636-40.
Although the crystal structure of troponin C is known (Herzberg, O., and James, M. N. G. (1985) Nature 313, 653-659; Sundaralingam, M., Bergstrom, R., Strasburg, G., Rao, S. T., Roychowdhury, P., Greaser, M., and Wang, B. C. (1985) Science 227, 945-948), its structure in solution, particularly under physiological conditions, has not been established. We examined the conformation of troponin C under a variety of conditions by measuring the distance between sites located in the N- and C-terminal domains using the technique of resonance energy transfer. The donor was the luminescent lanthanide ion Tb3+ bound at the low affinity metal sites in the N-terminal domain. The acceptor was 4-dimethylaminophenylazophenyl-4'-maleimide attached at Cys-98 in the C-terminal domain. The distance between these sites was found to be greater than 5.2 nm at pH 5.0, 2.7 nm at pH 6.8 for uncomplexed troponin C, and 4.1 nm for troponin C complexed with troponin I at pH 6.8. These findings suggest that uncomplexed troponin C undergoes a pH-dependent transition from an elongated conformation, compatible with the crystal structure at acidic pH, to a more compact conformation at neutral pH. When complexed with troponin I, troponin C adopts a conformation of intermediate length compared to the uncomplexed molecule at pH 6.8 and 5.0.
尽管肌钙蛋白C的晶体结构已为人所知（赫茨伯格，O.，和詹姆斯，M. N. G.（1985年）《自然》313卷，653 - 659页；桑达拉林加姆，M.，伯格斯特龙，R.，斯特拉斯堡，G.，拉奥，S. T.，罗伊乔杜里，P.，格雷泽，M.，和王，B. C.（1985年）《科学》227卷，945 - 948页），但其在溶液中的结构，尤其是在生理条件下的结构尚未确定。我们通过使用共振能量转移技术测量位于N端和C端结构域的位点之间的距离，在各种条件下研究了肌钙蛋白C的构象。供体是结合在N端结构域低亲和力金属位点的发光镧系离子Tb3 +。受体是连接在C端结构域中Cys - 98处的4 - 二甲基氨基苯基偶氮苯基 - 4'-马来酰亚胺。发现这些位点之间的距离在pH 5.0时大于5.2 nm，在pH 6.8时，未复合的肌钙蛋白C为2.7 nm，在pH 6.8时与肌钙蛋白I复合的肌钙蛋白C为4.1 nm。这些发现表明未复合的肌钙蛋白C经历了一个pH依赖性转变，从与酸性pH下的晶体结构相容的伸长构象转变为中性pH下更紧凑的构象。当与肌钙蛋白I复合时，在pH 6.8和5.0时，肌钙蛋白C与未复合分子相比采用中等长度的构象。
