Strong cross-bridges potentiate the Ca(2+) affinity changes produced by hypertrophic cardiomyopathy cardiac troponin C mutants in myofilaments: a fast kinetic approach.
This spectroscopic study examined the steady-state and kinetic parameters governing the cross-bridge effect on the increased Ca(2+) affinity of hypertrophic cardiomyopathy-cardiac troponin C (HCM-cTnC) mutants. Previously, we found that incorporation of the A8V and D145E HCM-cTnC mutants, but not E134D into thin filaments (TFs), increased the apparent Ca(2+) affinity relative to TFs containing the WT protein. Here, we show that the addition of myosin subfragment 1 (S1) to TFs reconstituted with these mutants in the absence of MgATP(2-), the condition conducive to rigor cross-bridge formation, further increased the apparent Ca(2+) affinity. Stopped-flow fluorescence techniques were used to determine the kinetics of Ca(2+) dissociation (k(off)) from the cTnC mutants in the presence of TFs and S1. At a high level of complexity (i.e. TF + S1), an increase in the Ca(2+) affinity and decrease in k(off) was achieved for the A8V and D145E mutants when compared with WT. Therefore, it appears that the cTnC Ca(2+) off-rate is most likely to be affected rather than the Ca(2+) on rate. At all levels of TF complexity, the results obtained with the E134D mutant reproduced those seen with the WT protein. We conclude that strong cross-bridges potentiate the Ca(2+)-sensitizing effect of HCM-cTnC mutants on the myofilament. Finally, the slower k(off) from the A8V and D145E mutants can be directly correlated with the diastolic dysfunction seen in these patients.
Department of Molecular and Cellular Pharmacology, Miller School of Medicine, University of Miami, Miami, Florida 33136, USA.
Jose Renato
JR
Pinto
Daniel P
DP
Reynaldo
Michelle S
MS
Parvatiyar
David
D
Dweck
Jingsheng
J
Liang
Michelle A
MA
Jones
Martha M
MM
Sorenson
James D
JD
Potter
D008841:Actin Cytoskeleton / Q000502:physiology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002312:Cardiomyopathy, Hypertrophic / Q000235:genetics / Q000378:metabolism / Q000503:physiopathology; D003432:Cross-Linking Reagents / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D016296:Mutagenesis; D009200:Myocardial Contraction / Q000502:physiology; D032383:Myocytes, Cardiac / Q000166:cytology / Q000502:physiology*; D015879:Myosin Subfragments / Q000378:metabolism; D011487:Protein Conformation; D011817:Rabbits; D013552:Swine; D019209:Troponin C / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
D003432:Cross-Linking Reagents; D015879:Myosin Subfragments; D019209:Troponin C; D002118:Calcium