Familial hypertrophic cardiomyopathy mutations in troponin I (K183D, G203S, K206Q) enhance filament sliding.
A major cause of familial hypertrophic cardiomyopathy (FHC) is dominant mutations in cardiac sarcomeric genes. Linkage studies identified FHC-related mutations in the COOH terminus of cardiac troponin I (cTnI), a region with unknown function in Ca(2+) regulation of the heart. Using in vitro assays with recombinant rat troponin subunits, we tested the hypothesis that mutations K183Delta, G203S, and K206Q in cTnI affect Ca(2+) regulation. All three mutants enhanced Ca(2+) sensitivity and maximum speed (s(max)) of filament sliding of in vitro motility assays. Enhanced s(max) (pCa 5) was observed with rabbit skeletal and rat cardiac (alpha-MHC or beta-MHC) heavy meromyosin (HMM). We developed a passive exchange method for replacing endogenous cTn in permeabilized rat cardiac trabeculae. Ca(2+) sensitivity and maximum isometric force did not differ between preparations exchanged with cTn(cTnI,K206Q) or wild-type cTn. In both trabeculae and motility assays, there was no loss of inhibition at pCa 9. These results are consistent with COOH terminus of TnI modulating actomyosin kinetics during unloaded sliding, but not during isometric force generation, and implicate enhanced cross-bridge cycling in the cTnI-related pathway(s) to hypertrophy.
Köhler
Jan
J
Molekular- und Zellphysiologie, Medizinische Hochschule, D-30625 Hannover, Germany.
Chen
Ying
Y
Brenner
Bernhard
B
Gordon
Albert M
AM
Kraft
Theresia
T
Martyn
Donald A
DA
Regnier
Michael
M
Rivera
Anthony J
AJ
Wang
Chien-Kao
CK
Chase
P Bryant
PB
D008841:Actin Cytoskeleton / Q000378:metabolism / Q000473:pathology* / Q000502:physiology; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution / Q000235:genetics*; D000818:Animals; D002118:Calcium / Q000502:physiology; D024741:Cardiomyopathy, Hypertrophic, Familial / Q000235:genetics* / Q000473:pathology; D002417:Cattle; D005973:Glutamine / Q000235:genetics; D005998:Glycine / Q000235:genetics; D008239:Lysine / Q000235:genetics; D008297:Male; D009206:Myocardium / Q000201:enzymology / Q000378:metabolism; D017354:Point Mutation; D011817:Rabbits; D051381:Rats; D017207:Rats, Sprague-Dawley; D011994:Recombinant Proteins / Q000235:genetics; D012518:Sarcomeres / Q000235:genetics / Q000502:physiology; D017384:Sequence Deletion / Q000235:genetics*; D012694:Serine / Q000235:genetics; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology; D019210:Troponin I / Q000235:genetics* / Q000502:physiology
D011994:Recombinant Proteins; D019210:Troponin I; D005973:Glutamine; D012694:Serine; D008239:Lysine; D002118:Calcium; D005998:Glycine