A dilated cardiomyopathy troponin C mutation lowers contractile force by reducing strong myosin-actin binding.
In this study we explore the mechanisms by which a double mutation (E59D/D75Y) in cardiac troponin C (CTnC) associated with dilated cardiomyopathy reduces the Ca(2+)-activated maximal tension of cardiac muscle. Studying the single mutants (i.e. E59D or D75Y) indicates that D75Y, but not E59D, causes a reduction in the calcium affinity of CTnC in troponin complex, regulated thin filaments (RTF), and the Ca(2+) sensitivity of contraction and ATPase in cardiac muscle preparations. However, both D75Y and E59D are required to reduce the actomyosin ATPase activity and maximal force in muscle fibers, indicating that E59D enhances the effects of D75Y. Part of the reduction in force/ATPase may be due to a defect in the interactions between CTnC and cardiac troponin T, which are known to be necessary for ATPase activation. An additional mechanism for the reduction in force/ATPase comes from measurements of the binding stoichiometry of myosin subfragment-1 (S-1) to the RTF. Using wild type RTFs, 4.8 mol S-1 was bound per mol filament (seven actins), whereas with E59D/D75Y RTFs, the number of binding sites was reduced by approximately 23% to 3.7. Altogether, these results suggest that the reduction in force and ATPase activation is possibly due to a thin filament conformation that promotes fewer accessible S-1-binding sites. In the absence of any family segregation data, the functional results presented here support the concept that this is likely a dilated cardiomyopathy-causing mutation.
T10 T11 T12 T13 T14 T15 T16 T17 T18 T19 T1 T20 T21 T22 T23 T24 T25 T26 T27 T28 T29 T2 T30 T31 T32 T33 T34 T35 T36 T37 T38 T39 T3 T4 T5 T6 T7 T8 T9
GENE-N GENE-N GENE-N GENE-N GENE-Y GENE-N GENE-N GENE-N GENE-N GENE-N CHEMICAL GENE-N GENE-N GENE-N GENE-N GENE-N GENE-N GENE-N GENE-N GENE-Y GENE-Y CHEMICAL GENE-N GENE-Y GENE-N GENE-N GENE-N GENE-N GENE-N GENE-Y GENE-N GENE-N GENE-N GENE-Y GENE-N GENE-N GENE-N GENE-N GENE-N
E59D D75Y D75Y E59D CTnC troponin regulated thin filaments RTF ATPase D75Y Ca(2+) E59D actomyosin ATPase E59D D75Y ATPase E59D D75Y CTnC cardiac troponin T Ca(2+) ATPase cardiac troponin C ATPase myosin subfragment-1 S-1 RTF RTFs troponin C myosin actin S-1 CTnC E59D D75Y RTFs ATPase S-1-binding sites