The influence of trout cardiac troponin I and PKA phosphorylation on the Ca2+ affinity of the cardiac troponin complex

Journal of Experimental Biology - Tập 214 Số 12 - Trang 1981-1988 - 2011
Kelly P. Kirkpatrick1, Alan Robertson1, Jordan M. Klaiman1, Todd E. Gillis1
1Department of Integrative Biology, University of Guelph, Guelph, On, Canada, N1G 2W1

Tóm tắt

SUMMARY The trout heart is 10-fold more sensitive to Ca2+ than the mammalian heart. This difference is due, in part, to cardiac troponin C (cTnC) from trout having a greater Ca2+ affinity than human cTnC. To determine what other proteins are involved, we cloned cardiac troponin I (cTnI) from the trout heart and determined how it alters the Ca2+ affinity of a cTn complex containing all mammalian components (mammalian cTn). Ca2+ activation of the complex was characterized using a human cTnC mutant that contains anilinonapthalenesulfote iodoacetamide attached to Cys53. When the cTn complex containing labeled human cTnC was titrated with Ca2+, its fluorescence changed, reaching an asymptote upon saturation. Our results reveal that trout cTnI lacks the N-terminal extension found in cTnI from all other vertebrate groups. This protein domain contains two targets (Ser23 and Ser24) for protein kinase A (PKA) and protein kinase C. When these are phosphorylated, the rate of cardiomyocyte relaxation increases. When rat cTnI in the mammalian cTn complex was replaced with trout cTnI, the Ca2+ affinity was increased ∼1.8-fold. This suggests that trout cTnI contributes to the high Ca2+ sensitivity of the trout heart. Treatment of the two cTn complexes with PKA decreased the Ca2+ affinity of both complexes. However, the change for the complex containing rat cTnI was 2.2-fold that of the complex containing trout cTnI. This suggests that the phosphorylation of trout cTnI does not play as significant a role in regulating cTn function in trout.

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Journal of Experimental Biology

Tập 214 Số 12

1981-1988

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