title: Biophysical properties of human β-cardiac myosin with converter mutations that cause hypertrophic cardiomyopathy.
abstract: Hypertrophic cardiomyopathy (HCM) affects 1 in 500 individuals and is an important cause of arrhythmias and heart failure. Clinically, HCM is characterized as causing hypercontractility, and therapies are aimed toward controlling the hyperactive physiology. Mutations in the β-cardiac myosin comprise ~40% of genetic mutations associated with HCM, and the converter domain of myosin is a hotspot for HCM-causing mutations; however, the underlying primary effects of these mutations on myosin's biomechanical function remain elusive. We hypothesize that these mutations affect the biomechanical properties of myosin, such as increasing its intrinsic force and/or its duty ratio and therefore the ensemble force of the sarcomere. Using recombinant human β-cardiac myosin, we characterize the molecular effects of three severe HCM-causing converter domain mutations: R719W, R723G, and G741R. Contrary to our hypothesis, the intrinsic forces of R719W and R723G mutant myosins are decreased compared to wild type and unchanged for G741R. Actin and regulated thin filament gliding velocities are ~15% faster for R719W and R723G myosins, whereas there is no change in velocity for G741R. Adenosine triphosphatase activities and the load-dependent velocity change profiles of all three mutant proteins are very similar to those of wild type. These results indicate that the net biomechanical properties of human β-cardiac myosin carrying these converter domain mutations are very similar to those of wild type or are even slightly hypocontractile, leading us to consider an alternative mechanism for the clinically observed hypercontractility. Future work includes how these mutations affect protein interactions within the sarcomere that increase the availability of myosin heads participating in force production.
authors.affiliation: Department of Biochemistry, Stanford University School of Medicine, Stanford, CA 94305, USA.; Department of Medicine, Division of Cardiovascular Medicine, Stanford University School of Medicine, Stanford, CA 94305, USA.
authors.forename: Masataka
authors.initials: M
authors.lastname: Kawana
authors.affiliation: Department of Biochemistry, Stanford University School of Medicine, Stanford, CA 94305, USA.
authors.forename: Saswata S
authors.initials: SS
authors.lastname: Sarkar
authors.affiliation: Department of Biochemistry, Stanford University School of Medicine, Stanford, CA 94305, USA.
authors.forename: Shirley
authors.identifier: 0000-0001-9044-3224
authors.initials: S
authors.lastname: Sutton
authors.affiliation: Department of Biochemistry, Stanford University School of Medicine, Stanford, CA 94305, USA.; Department of Pediatrics (Cardiology), Stanford University School of Medicine, Stanford, CA 94305, USA.
authors.forename: Kathleen M
authors.initials: KM
authors.lastname: Ruppel
authors.affiliation: Department of Biochemistry, Stanford University School of Medicine, Stanford, CA 94305, USA.
authors.forename: James A
authors.identifier: 0000-0002-4324-4254
authors.initials: JA
authors.lastname: Spudich
mesh_terms: D019943:Amino Acid Substitution; D006332:Cardiomegaly; D030342:Genetic Diseases, Inborn; D006801:Humans; D020125:Mutation, Missense; D024723:Ventricular Myosins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D024723:Ventricular Myosins
keywords: cardiac myosin; cardiomyopathy; contractility; converter domain; hypertrophic cardiomyopathy; myosin