Bovine cardiac troponin T: Amino acid sequences of the two isoforms

John Leszyk, Ranjana Dumaswala, James D. Potter, Nikolai B. Gusev, Alexandr D. Verin, Larry S. Tobacman, John H. Collins

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65 Scopus citations

Abstract

Troponin T (TnT) is the tropomyosin-binding subunit of troponin, the thin filament regulatory complex that confers calcium sensitivity to striated muscle contraction and actomyosin ATPase activity. Bovine cardiac muscle contains two isoforms (TnT-1 and TnT-2) of TnT that differ in sequence near their amino termini. Thin filaments containing TnT-2 require less calcium to activate the MgATPase rate of myosin than do thin filaments containing TnT-1. Using whole troponin T purified from adult bovine cardiac muscle, we have determined the complete amino acid sequence of the larger, more abundant isoform TnT-1. We confirmed that sequence differences between TnT-1 and TnT-2 are confined to the amino-terminal regions and found that TnT-1 makes up approximately 75% of the total troponin T isolated. Partial sequencing of the separated isoforms showed that the difference between them is due solely to residues 15-19 (Glu-Ala-Ala-Glu-Glu) of TnT-1 being absent from TnT-2. The deleted segment may correspond to the product of exon 4 of the chicken cardiac TnT gene [Cooper, T. A., & Ordahl, C. P. (1985) J. Biol. Chem. 260, 11140-11148]. Exon 5, which is developmentally regulated in the chicken, is not expressed in either TnT-1 or TnT-2. TnT-1 contains 284 amino acid residues and has a Mr of 33 808, while TnT-2 contains 279 amino acid residues and has a Mr of 33 279. Bovine cardiac TnT contains the only known thiol group in any isolated TnT (Cys-39 of TnT-1, Cys-34 of TnT-2). Comparison of bovine, rabbit, and chicken cardiac TnT sequences shows near identity of the amino-terminal 13 amino acid residues (exons 2 and 3 of the chicken cardiac gene), many differences in the following 60 residues (exons 4-8), and great similarity in the C-terminal 230 residues (exons 9-18).

Original languageEnglish
Pages (from-to)7035-7042
Number of pages8
JournalBiochemistry
Volume26
Issue number22
StatePublished - Dec 1 1987
Externally publishedYes

ASJC Scopus subject areas

  • Biochemistry

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    Leszyk, J., Dumaswala, R., Potter, J. D., Gusev, N. B., Verin, A. D., Tobacman, L. S., & Collins, J. H. (1987). Bovine cardiac troponin T: Amino acid sequences of the two isoforms. Biochemistry, 26(22), 7035-7042.