The NH2-terminal region of troponin T activates actomyosin ATPase with tropomyosin, while its globular domain blocks activation without Ca2+ and anchors the troponin C-I complex.
The contraction of skeletal muscle is regulated by Ca2+ binding to troponin C, which results in an internal reorganization of the interactions within the troponin-tropomyosin complex. Troponin T is necessary for Ca2+-dependent inhibition and activation of actomyosin. Troponin T consists of an extended NH2-terminal domain that interacts with tropomyosin and a globular COOH-terminal domain that interacts with tropomyosin, troponin I, and troponin C. In this study we used recombinant troponin T and troponin I fragments to delimit further the structural and regulatory interactions with the thin filament. Our results show the following: (i) the NH2-terminal region of troponin T activates the actomyosin ATPase in the presence of tropomyosin; (ii) the interaction of the globular domain of troponin T with the thin filament blocks ATPase activation in the absence of Ca2+; and (iii) the COOH-terminal region of the globular domain anchors the troponin C-troponin I binary complex to troponin T through a direct Ca2+-independent interaction with the NH2-terminal region of troponin I. This interaction is required for Ca2+-dependent activation of the actomyosin ATPase activity. Based on these results we propose a refined model for the troponin complex and its interaction with the thin filament.
Malnic et al. (Wed,) reported a other. Recombinant troponin T and troponin I fragments was evaluated on Actomyosin ATPase activity and structural interactions. The NH2-terminal region of troponin T activates actomyosin ATPase with tropomyosin, while its globular domain blocks activation without Ca2+ and anchors the troponin C-I complex.