Effects of cardiomyopathy-causing mutations in the coiled-coil regions in troponin core domain on the ATPase activity and physiological functions of myofibrils

Matsumoto, Fumiko; Maeda, Kayo*; Piroddi, N.*; Belus, A.*; Poggesi, C.*; Maeda, Yuichiro*; Fujiwara, Satoru

Hypertrophic cardiomyopathy (HCM) is an autosomal dominant cardiac disease resulting from mutations in genes encoding contractile proteins, including troponin. HMC is characterized by functional aberration on the force-pCa relationship. Only a few HMC-causing mutations have been mapped on the coiled-coil region in the Tn core. Here we focus on two mutations in this region, E244D and K247R of TnT. Whereas E244D has been reported to show an increase of the maximum level of ATPase activity without changing the Ca sensitivity (Yanaga et. al., 1999), the functional consequence of K247R mutation has not been analyzed. We showed from the ATPase measurements of myofibrils containing the mutants K247R that this mutation exhibits similar functional consequences to the mutation E244D. Moreover, in order to understand how the mutations at these residues cause functional aberrations, we prepared various mutants of TnT (E244D, E244M, E244A, E244K, K247R, K247E, and K247A), having various volumes and charges, and measured ATPase activity of myofibrils containing these mutants TnT. The effect of mutations on the maximum ATPase activity level was different from each other while the Ca sensitivity was unchanged. To gain insight into the relationship between the ATPase activity and (possible) structural changes caused by these mutations, we carried out energy minimization/molecular dynamics calculations based on the crystal structure of the Tn-core. The results suggested that the stable hydrogen bond network at this region is important for the "proper" function of Tn.