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Am J Physiol Cell Physiol 284: C1176-C1184, 2003. First published January 8, 2003; doi:10.1152/ajpcell.00339.2002
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Vol. 284, Issue 5, C1176-C1184, May 2003

Sequence mutations in teleost cardiac troponin C that are permissive of high Ca2+ affinity of site II

Todd E. Gillis1,2, Chris D. Moyes3, and Glen F. Tibbits2,4

1 Department of Biological Sciences and 2 Cardiac Membrane Research Lab, Simon Fraser University, Burnaby, British Columbia V5A 1S6; 3 Department of Biology, Queens University, Kingston, Ontario K7L 3N6; and 4 Cardiovascular Sciences, British Columbia Research Institute for Children's and Women's Health, Vancouver, British Columbia, Canada V5Z 4H4

Cardiac myofibrils isolated from trout heart have been demonstrated to have a higher sensitivity for Ca2+ than mammalian cardiac myofibrils. Using cardiac troponin C (cTnC) cloned from trout and mammalian hearts, we have previously demonstrated that this comparatively high Ca2+ sensitivity is due, in part, to trout cTnC (ScTnC) having twice the Ca2+ affinity of mammalian cTnC (McTnC) over a broad range of temperatures. The amino acid sequence of ScTnC is 92% identical to McTnC. To determine the residues responsible for the high Ca2+ affinity, the function of a number of ScTnC and McTnC mutants was characterized by monitoring an intrinsic fluorescent reporter that monitors Ca2+ binding to site II (F27W). The removal of the COOH terminus (amino acids 90-161) from ScTnC and McTnC maintained the difference in Ca2+ affinity between the truncated cTnC isoforms (ScNTnC and McNTnC). The replacement of Gln29 and Asp30 in ScNTnC with the corresponding residues from McNTnC, Leu and Gly, respectively, reduced Ca2+ affinity to that of McNTnC. These results demonstrate that Gln29 and Asp30 in ScTnC are required for the high Ca2+ affinity of site II.

myocyte contractility; Antarctic icefish; salmonid


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