title: Effects of troponin T cardiomyopathy mutations on the calcium sensitivity of the regulated thin filament and the actomyosin cross-bridge kinetics of human β-cardiac myosin.
abstract: Hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM) lead to significant cardiovascular morbidity and mortality worldwide. Mutations in the genes encoding the sarcomere, the force-generating unit in the cardiomyocyte, cause familial forms of both HCM and DCM. This study examines two HCM-causing (I79N, E163K) and two DCM-causing (R141W, R173W) mutations in the troponin T subunit of the troponin complex using human β-cardiac myosin. Unlike earlier reports using various myosin constructs, we found that none of these mutations affect the maximal sliding velocities or maximal Ca(2+)-activated ADP release rates involving the thin filament human β-cardiac myosin complex. Changes in Ca(2+) sensitivity using the human myosin isoform do, however, mimic changes seen previously with non-human myosin isoforms. Transient kinetic measurements show that these mutations alter the kinetics of Ca(2+) induced conformational changes in the regulatory thin filament proteins. These changes in calcium sensitivity are independent of active, cycling human β-cardiac myosin.
authors.affiliation: Department of Biochemistry, Stanford University School of Medicine, Stanford, California, United States of America.
authors.forename: Ruth F
authors.initials: RF
authors.lastname: Sommese
authors.affiliation: Department of Biochemistry, Stanford University School of Medicine, Stanford, California, United States of America.
authors.forename: Suman
authors.initials: S
authors.lastname: Nag
authors.affiliation: Department of Biochemistry, Stanford University School of Medicine, Stanford, California, United States of America.
authors.forename: Shirley
authors.initials: S
authors.lastname: Sutton
authors.affiliation: Department of Pharmaceutical Chemistry, University of California San Francisco, San Francisco, California, United States of America.
authors.forename: Susan M
authors.initials: SM
authors.lastname: Miller
authors.affiliation: Department of Biochemistry, Stanford University School of Medicine, Stanford, California, United States of America.
authors.forename: James A
authors.initials: JA
authors.lastname: Spudich
authors.affiliation: Department of Biochemistry, Stanford University School of Medicine, Stanford, California, United States of America ; Department of Pediatrics (Cardiology), Stanford University School of Medicine, Stanford, California, United States of America.
authors.forename: Kathleen M
authors.initials: KM
authors.lastname: Ruppel
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism*; D000205:Actomyosin / Q000378:metabolism*; D000328:Adult; D002118:Calcium / Q000378:metabolism*; D009202:Cardiomyopathies / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D002311:Cardiomyopathy, Dilated / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D002312:Cardiomyopathy, Hypertrophic / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D006801:Humans; D007700:Kinetics; D008958:Models, Molecular; D009154:Mutation; D015879:Myosin Subfragments / Q000378:metabolism; D017433:Protein Structure, Secondary; D014335:Tropomyosin / Q000378:metabolism; D020107:Troponin T / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D024723:Ventricular Myosins / Q000378:metabolism*
chemical_list: D015879:Myosin Subfragments; D014335:Tropomyosin; D020107:Troponin T; D000205:Actomyosin; D024723:Ventricular Myosins; D002118:Calcium