An R111C polymorphism in wild turkey cardiac troponin I accompanying the dilated cardiomyopathy-related abnormal splicing variant of cardiac troponin T with potentially compensatory effects
An R111C polymorphism in wild turkey cardiac troponin I accompanying the dilated cardiomyopathy-related abnormal splicing variant of cardiac troponin T with potentially compensatory effects
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DOI：
10.1074/jbc.m314225200
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发表时间：
2004-04-02
影响因子：
4.8
通讯作者：
Jin, JP
中科院分区：
文献类型：
--
作者：
Biesiadecki, BJ;Schneider, KL;Jin, JP
心肌收缩由 Ca2+ 通过肌钙蛋白复合物调节，该复合物由三个亚基组成：肌钙蛋白 C (TnC)、肌钙蛋白 T (TnT) 和肌钙蛋白 I (TnI)。我们之前报道过，患有扩张型心肌病的火鸡心脏 TnT 的异常剪接导致与 TnI 的结合亲和力更大。在本研究中，我们鉴定了野生火鸡心脏中心脏 TnI 的多态性。新型火鸡心脏 TnI 的 cDNA 克隆和测序揭示了单个氨基酸取代 R111C。禽类心脏 TnI 中的 Arg(111) 对应于哺乳动物中的 Lys。该残基在整个脊椎动物门的心肌和骨骼肌 TnIs 中都是保守的，这意味着其具有重要的功能。在心肌肌钙蛋白的部分晶体结构中，该氨基酸位于与 TnT 直接接触的 α 螺旋中。结构模型表明，在该位置用 Cys 替代 Arg 或 Lys 不会破坏肌钙蛋白的整体结构。为了评估 Arg 和 Cys 侧链之间不同大小和电荷的功能意义，使用大肠杆菌中表达的纯化火鸡心脏 TnI 进行了蛋白质结合测定。结果表明，R111C 取代降低了与 TnT 的结合亲和力，这可能是对心肌病相关心脏 TnT 剪接变体增加的 TnI 结合亲和力的潜在补偿。因此，野生火鸡群体中心脏 TnI Cys(111) 等位基因的固定和相应的功能效应反映了适应性值的增加，这表明了治疗 TnT 肌病的新靶点。
Cardiac muscle contraction is regulated by Ca2+ through the troponin complex consisting of three subunits: troponin C (TnC), troponin T (TnT), and troponin I (TnI). We reported previously that the abnormal splicing of cardiac TnT in turkeys with dilated cardiomyopathy resulted in a greater binding affinity to TnI. In the present study, we characterized a polymorphism of cardiac TnI in the heart of wild turkeys. cDNA cloning and sequencing of the novel turkey cardiac TnI revealed a single amino acid substitution, R111C. Arg(111) in avian cardiac TnI corresponds to a Lys in mammals. This residue is conserved in cardiac and skeletal muscle TnIs across the vertebrate phylum, implying a functional importance. In the partial crystal structure of cardiac troponin, this amino acid resides in an alpha-helix that directly contacts with TnT. Structural modeling indicates that the substitution of Cys for Arg or Lys at this position would not disrupt the global structure of troponin. To evaluate the functional significance of the different size and charge between the Arg and Cys side chains, protein-binding assays using purified turkey cardiac TnI expressed in Escherichia coli were performed. The results show that the R111C substitution lowered binding affinity to TnT, which is potentially compensatory to the increased TnI-binding affinity of the cardiomyopathy-related cardiac TnT splicing variant. Therefore, the fixation of the cardiac TnI Cys(111) allele in the wild turkey population and the corresponding functional effect reflect an increased fitness value, suggesting a novel target for the treatment of TnT myopathies.