Increased Ca2+ affinity of cardiac thin filaments reconstituted with cardiomyopathy-related mutant cardiac troponin I.
To understand the molecular mechanisms whereby cardiomyopathy-related cardiac troponin I (cTnI) mutations affect myofilament activity, we have investigated the Ca2+ binding properties of various assemblies of the regulatory components that contain one of the cardiomyopahty-related mutant cTnI. Acto-S1 ATPase activities in reconstituted systems were also determined. We investigated R145G and R145W mutations from the inhibitory region and D190H and R192H mutations from the second actin-tropomyosin-binding site. Each of the four mutations sensitized the acto-S1 ATPase to Ca2+. Whereas the mutations from the inhibitory region increased the basal level of ATPase activity, those from the second actin-tropomyosin-binding site did not. The effects on the Ca2+ binding properties of the troponin ternary complex and the troponin-tropomyosin complex with one of four mutations were either desensitization or no effect compared with those with wild-type cTnI. All of the mutations, however, affected the Ca2+ sensitivities of the reconstituted thin filaments in the same direction as the acto-S1 ATPase activity. Also the thin filaments with one of the mutant cTnIs bound Ca2+ with less cooperativity compared with those with wild-type cTnI. These data indicate that the mutations found in the inhibitory region and those from the second actin-tropomyosin site shift the equilibrium of the states of the thin filaments differently. Moreover, the increased Ca2+ bound to myofilaments containing the mutant cTnIs may be an important factor in triggered arrhythmias associated with the cardiomyopathy.
Kobayashi
Tomoyoshi
T
Department of Physiology and Biophysics and Center for Cardiovascular Research, College of Medicine, University of Illinois, Chicago, Illinois 60612. Electronic address: tkoba@uic.edu.
Solaro
R John
RJ
Department of Physiology and Biophysics and Center for Cardiovascular Research, College of Medicine, University of Illinois, Chicago, Illinois 60612.
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D009202:Cardiomyopathies / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D051379:Mice; D009206:Myocardium / Q000378:metabolism*; D011485:Protein Binding; D019210:Troponin I / Q000235:genetics* / Q000378:metabolism*
D019210:Troponin I; D002118:Calcium