Modulation of the picosecond dynamics of troponin by the cardiomyopathy-causing mutation K247R of troponin T observed by quasielastic neutron scattering.

Troponin (Tn), consisting of three subunits (TnC, TnI, and TnT), regulates cardiac muscle contraction in a Ca2+ -dependent manner. Various point mutations of human cardiac Tn are known to cause familial hypertrophic cardiomyopathy due to aberration of the regulatory function. In this study, we investigated the effects of one of these mutations, K247R of TnT, on the picosecond dynamics of the Tn core domain (Tn-CD), consisting of TnC, TnI and TnT2 (183-288 residues of TnT), by carrying out the quasielastic neutron scattering measurements on the reconstituted Tn-CD containing either the wild-type TnT2 (wtTn-CD) or the mutant TnT2 (K247R-Tn-CD) in the absence and presence of Ca2+ . It was found that Ca2+ -binding to the wtTn-CD decreases the residence time of atomic motions in the Tn-CD with slight changes in amplitudes, suggesting that the regulatory function mainly requires modulation of frequency of atomic motions. On the other hand, the K247R-Tn-CD shows different dynamic behavior from that of the wtTn-CD both in the absence and presence of Ca2+ . In particular, the K247R-Tn-CD exhibits a larger amplitude than the wtTn-CD in the presence of Ca2+ , suggesting that the mutant can explore larger conformational space than the wild-type. This increased flexibility should be relevant to the functional aberration of this mutant.