Functional consequences of a carboxyl terminal missense mutation Arg278Cys in human cardiac troponin T.
A carboxyl terminal missense mutant Arg278Cys of human cardiac troponin T that causes familial hypertrophic cardiomyopathy was expressed in Escherichia coli, purified, and exchanged into rabbit cardiac skinned muscle fibers using a troponin exchange technique. Compared to the fibers exchanged with human cardiac wild-type troponin T, the fibers exchanged with the mutant Arg278Cys developed less maximum force with a decreased cooperativity and a slightly increased Ca(2+) sensitivity, resulting in a significant elevation of sub-half-maximal force. Since intact cardiac muscle is thought to never be activated beyond the half-maximum level, the results suggest that an enhanced myofilament response to Ca(2+) may be responsible for the pathogenesis of hypertrophic cardiomyopathy associated with this mutation. The results also provide the first evidence that the carboxyl terminal region of cardiac troponin T plays an important role probably through its interaction with tropomyosin in allowing troponin complex to inhibit the muscle contraction at low Ca(2+), in agreement with the hypothesis deduced from the previous studies on fast skeletal troponin T.
Morimoto
S
S
Faculty of Medicine, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka, 812-8582, Japan.
Nakaura
H
H
Yanaga
F
F
Ohtsuki
I
I
D008841:Actin Cytoskeleton / Q000187:drug effects / Q000502:physiology; D019943:Amino Acid Substitution; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002312:Cardiomyopathy, Hypertrophic / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics; D006801:Humans; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000187:drug effects; D018656:Muscle Fibers, Fast-Twitch / Q000502:physiology; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D020125:Mutation, Missense; D009206:Myocardium / Q000166:cytology*; D020033:Protein Isoforms; D011817:Rabbits; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D020107:Troponin T / Q000096:biosynthesis / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*
D020033:Protein Isoforms; D011994:Recombinant Proteins; D020107:Troponin T; D002118:Calcium