Sequence mutations in teleost cardiac troponin C that are permissive of high Ca2+ affinity of site II |
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Authors: | Gillis Todd E Moyes Chris D Tibbits Glen F |
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Institution: | Department of Biological Sciences, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada. |
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Abstract: | Cardiac myofibrilsisolated from trout heart have been demonstrated to have a highersensitivity for Ca2+ than mammalian cardiac myofibrils.Using cardiac troponin C (cTnC) cloned from trout and mammalian hearts,we have previously demonstrated that this comparatively highCa2+ 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 is92% identical to McTnC. To determine the residues responsible for thehigh Ca2+ affinity, the function of a number of ScTnC andMcTnC mutants was characterized by monitoring an intrinsic fluorescentreporter that monitors Ca2+ binding to site II (F27W). Theremoval of the COOH terminus (amino acids 90-161) from ScTnC andMcTnC maintained the difference in Ca2+ affinity betweenthe truncated cTnC isoforms (ScNTnC and McNTnC). The replacement ofGln29 and Asp30 in ScNTnC with thecorresponding residues from McNTnC, Leu and Gly, respectively, reducedCa2+ affinity to that of McNTnC. These results demonstratethat Gln29 and Asp30 in ScTnC are required forthe high Ca2+ affinity of site II. |
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