Altered regulation of cardiac muscle contraction by troponin T mutations that cause familial hypertrophic cardiomyopathy.
To study the effect of troponin (Tn) T mutations that cause familial hypertrophic cardiomyopathy (FHC) on cardiac muscle contraction, wild-type, and the following recombinant human cardiac TnT mutants were cloned and expressed: I79N, R92Q, F110I, E163K, R278C, and intron 16(G(1) --> A) (In16). These TnT FHC mutants were reconstituted into skinned cardiac muscle preparations and characterized for their effect on maximal steady state force activation, inhibition, and the Ca(2+) sensitivity of force development. Troponin complexes containing these mutants were tested for their ability to regulate actin-tropomyosin(Tm)-activated myosin-ATPase activity. TnT(R278C) and TnT(F110I) reconstituted preparations demonstrated dramatically increased Ca(2+) sensitivity of force development, while those with TnT(R92Q) and TnT(I79N) showed a moderate increase. The deletion mutant, TnT(In16), significantly decreased both the activation and the inhibition of force, and substantially decreased the activation and the inhibition of actin-Tm-activated myosin-ATPase activity. ATPase activation was also impaired by TnT(F110I), while its inhibition was reduced by TnT(R278C). The TnT(E163K) mutation had the smallest effect on the Ca(2+) sensitivity of force; however, it produced an elevated activation of the ATPase activity in reconstituted thin filaments. These observed changes in the Ca(2+) regulation of force development caused by these mutations would likely cause altered contractility and contribute to the development of FHC.
Szczesna
D
D
Department of Molecular Pharmacology, University of Miami School of Medicine, Miami, Florida 33101, USA.
Zhang
R
R
Zhao
J
J
Jones
M
M
Guzman
G
G
Potter
J D
JD
D000595:Amino Acid Sequence; D002118:Calcium / Q000494:pharmacology; D002312:Cardiomyopathy, Hypertrophic / Q000235:genetics*; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D006801:Humans; D066298:In Vitro Techniques; D008969:Molecular Sequence Data; D009119:Muscle Contraction; D018485:Muscle Fibers, Skeletal / Q000502:physiology; D009154:Mutation; D009200:Myocardial Contraction / Q000187:drug effects / Q000502:physiology*; D009218:Myosins / Q000037:antagonists & inhibitors / Q000378:metabolism; D020107:Troponin T / Q000235:genetics*
D020107:Troponin T; D009218:Myosins; D002118:Calcium