Sorsa T, Pollesello P, Permi P, Drakenberg T, Kilpeläinen I
Structural Biology, Drug Discovery Technologies, Orion Pharma, P.O. Box 65, 02101 Espoo, Finland.
J Mol Cell Cardiol. 2003 Sep;35(9):1055-61. doi: 10.1016/s0022-2828(03)00178-0.
The interaction between troponin C (TnC) and troponin I (TnI) is essential for the regulation of muscle contraction. There are several binding sites for TnI on TnC that are differentially occupied depending on the phase of the contraction/relaxation cycle. TnI and TnC interact in an antiparallel fashion with each other. The C-domain of cTnC and the N-domain region of cTnI(residues 33-70) always interact under physiological conditions, whereas the interaction between regulatory regions of TnC and TnI (residues 128-166) is calcium dependent. Previously, it has been shown that levosimendan, a calcium sensitizer used as a treatment for acute heart failure, can interact with both domains of isolated cTnC. To understand which interaction is relevant for the mechanism of calcium sensitization, we used a more complete troponin model obtained by complexing cTnI(32-79) and cTnI(128-180) with calcium-saturated cTnC(CS). The cTnI peptides bound to cTnC(CS) to form a 1:1:1 complex. The interaction of levosimendan with this complex was followed by 1H-(15)N heteronuclear correlation spectroscopy. It was clear that based on chemical shift changes, cTnI(32-79) blocked the levosimendan interaction sites on the C-domain, whereas cTnI(128-180) did not compete with levosimendan for the binding site on the N-domain. Hence, the effective binding site of levosimendan on cTnC resulting in the calcium-sensitizing effect is located in the regulatory domain (N-domain).
肌钙蛋白C（TnC）与肌钙蛋白I（TnI）之间的相互作用对于肌肉收缩的调节至关重要。TnC上有几个TnI的结合位点，它们在收缩/舒张周期的不同阶段被不同程度占据。TnI和TnC以反平行方式相互作用。在生理条件下，肌钙蛋白C（cTnC）的C结构域和肌钙蛋白I（cTnI）的N结构域区域（第33 - 70位氨基酸残基）总是相互作用，而TnC和TnI调节区域（第128 - 166位氨基酸残基）之间的相互作用则依赖于钙。此前已表明，作为治疗急性心力衰竭的钙增敏剂左西孟旦可与分离的cTnC的两个结构域相互作用。为了解哪种相互作用与钙增敏机制相关，我们使用了一个更完整的肌钙蛋白模型，该模型通过将cTnI(32 - 79)和cTnI(128 - 180)与钙饱和的cTnC（CS）复合获得。cTnI肽与cTnC(CS)结合形成1:1:1复合物。通过1H-(15)N异核相关光谱研究了左西孟旦与该复合物的相互作用。很明显，基于化学位移变化，cTnI(32 - 79)阻断了左西孟旦在C结构域上的相互作用位点，而cTnI(128 - 180)并不与左西孟旦竞争N结构域上的结合位点。因此，左西孟旦在cTnC上导致钙增敏作用的有效结合位点位于调节结构域（N结构域）。
