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J Biol Chem. 2015 Mar 13;290(11):7003-15. doi: 10.1074/jbc.M114.596676. Epub 2014 Dec 29.

Mechanistic heterogeneity in contractile properties of α-tropomyosin (TPM1) mutants associated with inherited cardiomyopathies.

Author information

1
From the Institute for Stem Cell Biology and Regenerative Medicine, Bangalore 560065, India.
2
From the Institute for Stem Cell Biology and Regenerative Medicine, Bangalore 560065, India, the National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560065, India.
3
From the Institute for Stem Cell Biology and Regenerative Medicine, Bangalore 560065, India, the Manipal University, Madhav Nagar, Manipal 576104, India.
4
the Council for Scientific and Industrial Research-Centre for Cellular and Molecular Biology, Hyderabad 500007, India.
5
the National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560065, India.
6
the Department of Biochemistry, Stanford University School of Medicine, Stanford, California 94305, and.
7
From the Institute for Stem Cell Biology and Regenerative Medicine, Bangalore 560065, India, the Department of Biochemistry, Stanford University School of Medicine, Stanford, California 94305, and.
8
From the Institute for Stem Cell Biology and Regenerative Medicine, Bangalore 560065, India, the McLaughlin Research Institute, Great Falls, Montana 59405 jam@instem.res.in.

Abstract

The most frequent known causes of primary cardiomyopathies are mutations in the genes encoding sarcomeric proteins. Among those are 30 single-residue mutations in TPM1, the gene encoding α-tropomyosin. We examined seven mutant tropomyosins, E62Q, D84N, I172T, L185R, S215L, D230N, and M281T, that were chosen based on their clinical severity and locations along the molecule. The goal of our study was to determine how the biochemical characteristics of each of these mutant proteins are altered, which in turn could provide a structural rationale for treatment of the cardiomyopathies they produce. Measurements of Ca(2+) sensitivity of human β-cardiac myosin ATPase activity are consistent with the hypothesis that hypertrophic cardiomyopathies are hypersensitive to Ca(2+) activation, and dilated cardiomyopathies are hyposensitive. We also report correlations between ATPase activity at maximum Ca(2+) concentrations and conformational changes in TnC measured using a fluorescent probe, which provide evidence that different substitutions perturb the structure of the regulatory complex in different ways. Moreover, we observed changes in protein stability and protein-protein interactions in these mutants. Our results suggest multiple mechanistic pathways to hypertrophic and dilated cardiomyopathies. Finally, we examined a computationally designed mutant, E181K, that is hypersensitive, confirming predictions derived from in silico structural analysis.

KEYWORDS:

Actin; Cardiac Hypertrophy; Cardiomyopathy; Myosin; Regulated Thin Filament; Tropomyosin

PMID:
25548289
PMCID:
PMC4358124
DOI:
10.1074/jbc.M114.596676
[Indexed for MEDLINE]
Free PMC Article

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