1. Altered regulatory function of two familial hypertrophic cardiomyopathy troponin T mutants
- Author
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Lily Tong, Christine E. Seidman, Poushali Mukherjea, Jonathan G. Seidman, and Sarah E. Hitchcock-DeGregori
- Subjects
medicine.medical_specialty ,Mutant ,Molecular Sequence Data ,Disease ,Myosins ,Biochemistry ,Troponin T ,Ventricular hypertrophy ,Internal medicine ,medicine ,Animals ,Humans ,Amino Acid Sequence ,Gene ,Sequence Deletion ,Familial Hypertrophic Cardiomyopathy ,business.industry ,Myocardium ,Troponin I ,food and beverages ,Cardiomyopathy, Hypertrophic ,medicine.disease ,Peptide Fragments ,Rats ,Enzyme Activation ,Premature death ,cardiovascular system ,Cardiology ,Calcium ,business ,Function (biology) ,Protein Binding - Abstract
Mutations in the gene encoding human cardiac troponin T can cause familial hypertrophic cardiomyopathy, a disease that is characterized by ventricular hypertrophy and sudden, premature death. Troponin T is the tropomyosin-binding subunit of troponin required for thin filament regulation of contraction. One mutation, a change in the intron 15 splice donor site, results in two truncated forms of troponin T [Thierfelder et al. (1994) Cell 77, 701-712]. In one form, the mRNA skips exon 16 that encodes the C-terminal 14 amino acids; in the other, seven novel residues replace the exon 15- and 16-encoded C-terminal 28 amino acids. The two troponin T cDNAs were expressed in Escherichia coli for functional analysis. Both C-terminal deletion mutants formed a complex with cardiac troponin C and troponin I that exhibited the same concentration dependence as wild-type for regulation of the actomyosin MgATPase. However, both mutants showed severely reduced activation of the regulated actomyosin in the presence of Ca2+, though the inhibition in the absence of Ca2+ and the Ca(2+)-dependence of activation were not altered. The C-terminal deletions reduce the effectiveness of Ca(2+)-troponin to switch the thin filament from the "off" to the "on" state. Both mutant troponin Ts have reduced affinity for troponin I; the shorter mutant is at least 6-fold weaker than wild-type. The low level of activation of the ATPase would be consistent with reduced contractile performance, and the results suggest reduced troponin I affinity may be the molecular basis for the disease.
- Published
- 1999