Alterations in Thin Filament Regulation Induced by a Human Cardiac Troponin T Mutant That Causes Dilated Cardiomyopathy Are Distinct from Those Induced by Troponin T Mutants That Cause Hypertrophic Cardiomyopathy

• Published in: The Journal of biological chemistry Vol. 277; no. 43; pp. 40710 - 40716
• Main Authors: Robinson, Paul, Mirza, Mahmooda, Knott, Adam, Abdulrazzak, Hassan, Willott, Ruth, Marston, Steven, Watkins, Hugh, Redwood, Charles
• Format: Journal Article
• Language: English
• Published: United States American Society for Biochemistry and Molecular Biology 25-10-2002
• Subjects: Actin Cytoskeleton - metabolism; Adenosine Triphosphatases - metabolism; Animals; Calcium - metabolism; Cardiomegaly - etiology; Cardiomegaly - genetics; Cardiomyopathy, Dilated - etiology; Cardiomyopathy, Dilated - genetics; Humans; Mutation; Myocardium - enzymology; Myocardium - metabolism; Rabbits; Troponin T - genetics; Troponin T - physiology
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M203446200

We have compared the in vitro regulatory properties of recombinant human cardiac troponin reconstituted using wild type troponin T with troponin containing
the ΔLys-210 troponin T mutant that causes dilated cardiomyopathy (DCM) and the R92Q troponin T known to cause hypertrophic
cardiomyopathy (HCM). Troponin containing ΔLys-210 troponin T inhibited actin-tropomyosin-activated myosin subfragment-1 ATPase
activity to the same extent as wild type at p Ca8.5 (>80%) but produced substantially less enhancement of ATPase at p Ca4.5. The Ca 2+ sensitivity of ATPase activation was increased (Δ p Ca 50 = +0.2 p Ca units) and cooperativity of Ca 2+ activation was virtually abolished. Equimolar mixtures of wild type and ΔLys-210 troponin T gave a lower Ca 2+ sensitivity than with wild type, while maintaining the diminished ATPase activation at p Ca4.5 observed with 100% mutant. In contrast, R92Q troponin gave reduced inhibition at p Ca8.5 but greater activation than wild type at p Ca4.5; Ca 2+ sensitivity was increased but there was no change in cooperativity. In vitro motility assay of reconstituted thin filaments confirmed the ATPase results and moreover indicated that the predominant effect
of the ΔLys-210 mutation was a reduced sliding speed. The functional consequences of this DCM mutation are qualitatively different
from the R92Q or any other studied HCM troponin T mutation, suggesting that DCM and HCM may be triggered by distinct primary
stimuli.