Troponin is the regulatory complex of the myofibrillar thin filament that plays a critical role in regulating excitation-contraction coupling in the heart. Troponin is composed of three distinct gene products: troponin C (cTnC), the 18-kD Ca(2+)-binding subunit; troponin I (cTnI), the approximately 23-kD inhibitory subunit that prevents contraction in the absence of Ca2+ binding to cTnC; and troponin T (cTnT), the approximately 35-kD subunit that attaches troponin to tropomyosin (Tm) and to the myofibrillar thin filament. Over the past 45 years, extensive biochemical, biophysical, and structural studies have helped to elucidate the molecular basis of troponin function and thin filament activation in the heart. At the onset of systole, Ca2+ binds to the N-terminal Ca2+ binding site of cTnC initiating a conformational change in cTnC, which catalyzes protein-protein associations activating the myofibrillar thin filament. Thin filament activation in turn facilitates crossbridge cycling, myofibrillar activation, and contraction of the heart. The intrinsic length-tension properties of cardiac myocytes as well as the Frank-Starling properties of the intact heart are mediated primarily through Ca(2+)-responsive thin filament activation. cTnC, cTnI, and cTnT are encoded by distinct single-copy genes in the human genome, each of which is expressed in a unique cardiac-restricted developmentally regulated fashion. Elucidation of the transcriptional programs that regulate troponin transcription and gene expression has provided insights into the molecular mechanisms that regulate and coordinate cardiac myocyte differentiation and provided unanticipated insights into the pathogenesis of cardiac hypertrophy. Autosomal dominant mutations in cTnI and cTnT have been identified and are associated with familial hypertrophic and restrictive cardiomyopathies.

中文翻译：

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心肌细胞中肌钙蛋白复合物的生物学。

肌钙蛋白是肌原纤维细丝的调节复合物，在调节心脏的兴奋收缩耦合中起关键作用。肌钙蛋白由三个不同的基因产物组成：肌钙蛋白C（cTnC），18-kD Ca（2+）结合亚基；肌钙蛋白I（cTnI），约23 kD抑制性亚基，可在没有Ca2 +与cTnC结合的情况下防止收缩。肌钙蛋白T（cTnT），约35kD的亚基，将肌钙蛋白与原肌球蛋白（Tm）和肌原纤维细丝相连。在过去的45年中，广泛的生化，生物物理和结构研究已帮助阐明了肌钙蛋白功能和心脏细丝活化的分子基础。在收缩期开始时，Ca2 +与cTnC的N端Ca2 +结合位点结合，从而引发cTnC的构象变化，催化蛋白质-蛋白质缔合，激活肌原纤维细丝。细丝激活反过来又促进了跨桥循环，肌原纤维激活和心脏收缩。心肌细胞的固有长度-张力特性以及完整心脏的Frank-Starling特性主要是通过Ca（2+）响应性细丝激活来介导的。cTnC，cTnI和cTnT由人类基因组中不同的单拷贝基因编码，每个基因均以独特的受心脏限制的发育调控方式表达。对调节肌钙蛋白转录和基因表达的转录程序的阐明为调节和协调心肌细胞分化的分子机制提供了见识，并为心脏肥大的发病机理提供了意想不到的见解。已经鉴定出cTnI和cTnT的常染色体显性突变，并与家族性肥厚性和限制性心肌病相关。