Mutations in human cardiac Troponin I that are associated with restrictive cardiomyopathy affect basal ATPase activity and the calcium sensitivity of force development
Mutations in human cardiac Troponin I that are associated with restrictive cardiomyopathy affect basal ATPase activity and the calcium sensitivity of force development
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DOI：
10.1074/jbc.m500287200
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发表时间：
2005-09-02
影响因子：
4.8
通讯作者：
Potter, JD
中科院分区：
文献类型：
--
作者：
Gomes, AV;Liang, JS;Potter, JD
人心肌肌钙蛋白I(CTnI)是第一个突变与限制性心肌病相关的肌瘤蛋白。为了确定与限制性心肌病相关的5个cTnI突变(L144Q、R145W、A171T、K178E和R192H)与引起肥厚性心肌病的cTnI突变是否有区别，进行了肌动球蛋白ATPase活性和皮肤纤维的研究。与野生型cTnI相比，所研究的所有五个突变都显示出力量发育对钙的敏感性增加。临床表型最差的两个突变(K178E和R192H)均显示钙敏感性显著增加(Delta PCA(50)分别为0.47和0.36)。虽然这些突变中至少有一个不在cTnI已知的抑制区，但所有被研究的突变都导致cTnI抑制肌动蛋白ATPase活性的能力下降。野生型和突变型cTnI混合后，在肌动球蛋白ATPase活性测定中，突变型cTnI可分为三类：显性(L144Q、A171T和R192H)、等价型(K178E)和弱型(R145W)。虽然大多数突变体都能激活肌动球蛋白ATPase，但L144Q的最大ATPase活性明显低于其他突变体或野生型cTnI。三个突变体(L144Q、R145W和K178E)在没有钙离子的情况下不能完全松弛收缩。被研究的五个cTnI突变不能完全抑制ATPase活性/力量的发育，并且钙敏感性的增加通常比大多数肥厚型心肌病突变的观察到的更大，这可能会导致严重的舒张性功能障碍，并可能是导致某些基因影响个体限制性心肌病表型的主要生理因素。
Human cardiac Troponin I (cTnI) is the first sarcomeric protein for which mutations have been associated with restrictive cardiomyopathy. To determine whether five mutations in cTnI (L144Q, R145W, A171T, K178E, and R192H) associated with restrictive cardiomyopathy were distinguishable from hypertrophic cardiomyopathy-causing mutations in cTnI, actomyosin ATPase activity and skinned fiber studies were carried out. All five mutations investigated showed an increase in the Ca2+ sensitivity of force development compared with wildtype cTnI. The two mutations with the worst clinical phenotype (K178E and R192H) both showed large increases in Ca2+ sensitivity (Delta pCa(50) = 0.47 and 0.36, respectively). Although at least one of these mutations is not in the known inhibitory regions of cTnI, all of the mutations investigated caused a decrease in the ability of cTnI to inhibit actomyosin ATPase activity. Mixtures of wild-type and mutant cTnI showed that cTnI mutants could be classified into three different groups: dominant (L144Q, A171T and R192H), equivalent (K178E), or weaker (R145W) than wild-type cTnI in actomyosin ATPase assays in the absence of Ca2+. Although most of the mutants were able to activate actomyosin ATPase similarly to wild-type cTnI, L144Q had significantly lower maximal ATPase activities than any of the other mutants or wild-type cTnI. Three mutants (L144Q, R145W, and K178E) were unable to fully relax contraction in the absence of Ca2+. The inability of the five cTnI mutations investigated to fully inhibit ATPase activity/force development and the generally larger increases in Ca2+ sensitivity than observed for most hypertrophic cardiomyopathy mutations would likely lead to severe diastolic dysfunction and may be the major physiological factors responsible for causing the restrictive cardiomyopathy phenotype in some of the genetically affected individuals.