Cardiac troponin C binds to cardiac troponin T independently of bivalent cations, suggesting the troponin C-T interaction does not play a major role in troponin regulation of muscle contraction.
May indicate limited regulatory role for cardiac troponin C-T binding; hypothesis-generating for isoform differences, requires validation.
1) We investigated the interactions between troponin C and troponin T, and between calmodulin and troponin T, in the presence of Ca2+ and Sr2+. Polyacrylamidegel electrophoresis under non-denaturing conditions and ultracentrifugation methods was used to examine the interactions. Calmodulin and skeletal troponin C bound to skeletal troponin T only in the presence of bivalent cations, whereas calmodulin and cardiac troponin C bound to cardiac troponin T in both the presence and absence of bivalent cations. 2) Skeletal troponin C bound to the skeletal troponin T-tropomyosin-actin complex only in the presence of bivalent cations, although cardiac troponin C hardly bound to the cardiac troponin T-tropomyosin-actin complex even in the presence of bivalent cations. 3) Calmodulin bound to the skeletal and cardiac troponin T-tropomyosin-actin complexes only in the presence of bivalent cations. 4) Trifluoperazine, a calmodulin antagonist, inhibited the bivalentcation-dependent interaction between calmodulin and skeletal troponin T. 5) The results suggest that the conformation of cardiac troponin T coupled with the tropomyosin-actin complex differs considerably from that of troponin T alone, and that the interaction between troponin C and troponin T does not play a major role in the troponin regulation of muscle contraction. The bivalent-cation-induced exposure of the hydrophobic region may enable calmodulin to bind to skeletal troponin T.
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Yamamoto et al. (1987) studied this question.
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