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Am J Physiol Cell Physiol (January 8, 2003). doi:10.1152/ajpcell.00339.2002
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Submitted on July 23, 2002
Accepted on December 11, 2002

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

Todd E Gillis1, Christopher D Moyes2, and Glen F Tibbits3*

1 Biological Sciences, Simon Fraser University, Burnaby, BC, Canada; Cardiac Membrane Research Lab, Simon Fraser University, Burnaby, BC, Canada
2 Biology, Queen's University, Kingston, ON, Canada
3 Cardiac Membrane Research Lab, Simon Fraser University, Burnaby, BC, Canada; Cardiovascular Sciences, BC Research Institute for Children's and Women's Health, Vancouver, BC, Canada; Biological Sciences, Simon Fraser University, Burnaby, BC, Canada

* To whom correspondence should be addressed. E-mail: tibbits{at}sfu.ca.

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 in 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 were characterized by monitoring an intrinsic fluorescent reporter that reflects Ca2+ binding to site II (F27W). The removal of the C-terminus (aa 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.




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