The interaction of troponin‐I with the N‐terminal region of actin

The interaction between troponin‐I and actin that underlies thin‐filament regulation in striated muscle has been studied using proton magnetic resonance spectroscopy. A restricted portion of skeletal muscle troponin‐I (residues 96–116) has previously been shown to be capable of inhibiting the MgATPase activity of actomyosin in a manner enhanced by tropomyosin [Syska et al. (1976) Biochem. J. 153, 375–387]. On the basis of homologous spectral effects for signals of specific groups observed in different complexes formed using the native proteins and a variety of defined peptides, it is concluded that the segment of troponin‐I which has inhibitory activity interacts with the N‐terminal region of actin. The surface of contact of the inhibitory segment of troponin‐I with actin involves two regions of the N‐terminal of actin. These are located between residues 1–7 and 19–44. The data are discussed in the context of a structural mechanism for the inhibition of myosin ATPase activation.