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

Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106-4970.
Journal of Biological Chemistry (Impact Factor: 4.57). 05/2004; 279(14):13825-32. DOI: 10.1074/jbc.M314225200
Source: PubMed

ABSTRACT Cardiac muscle contraction is regulated by Ca(2+) 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.

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    • "Although this mutation was not observed in this work, the novel cTnT SNPs and haplotypes presented here provide resources that can be used to investigate, by association, the link between cTnT and DCM and other diseases and abnormalities. The cTnT SNPs are distinct from the nonsynonymous nucleotide variant described by Biesiadecki et al. (2004) in 1 of the 3 subunits of the troponin complex, troponin I. An amino acid substitution, known as the R111C polymorphism, that involves Arg and Cys residues lowers troponin I binding affinity to troponin T, the molecule investigated in this work. "
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    ABSTRACT: Determining variation in genes is fundamental to understanding their function in the disease state. Cardiac troponin T (cTnT) and phospholamban (PLN) genes have been implicated in dilated cardiomyopathy (DCM) in human and model species. To investigate the role of these 2 candidate genes in DCM in the turkey Meleagris gallopavo, understanding sequence variants and map position distribution is necessary. To this end, a total of 1854 and 1771 bp of cTnT and PLN gene sequences, respectively, were scanned for single nucleotide polymorphisms (SNPs) in a randomly bred population. A total of 15 SNPs was identified in the cTnT and PLN genomic sequences. Nine haplotypes, 5 in cTnT and 4 in PLN, were identified. Observed heterozygosities (0.02-0.39) in the turkey population were low for both genes. Within each gene, 1 SNP corresponding to a restriction enzyme site was identified and used to develop a PCR-restriction fragment length polymorphism (RFLP) genotyping assay. The PLN gene was genetically mapped to turkey chromosome 2, equivalent to Gallus gallus chromosome 3, and cTnT mapped to a turkey microchromosome. Although limited because of the relatively small sample size of 55 birds, the data from this SNP analysis of PLN and cTnT provide a foundation from which to evaluate the function of cTnT and PLN in the turkey. Information about the distribution of the SNPs and haplotypes will facilitate future association and linkage studies.
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    Journal of Biological Chemistry 03/2005; 280(8):6602-9. DOI:10.1074/jbc.M408525200 · 4.57 Impact Factor
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