title: Ablation of cardiac myosin binding protein-C disrupts the super-relaxed state of myosin in murine cardiomyocytes.
abstract: Cardiac myosin binding protein-C (cMyBP-C) is a structural and regulatory component of cardiac thick filaments. It is observed in electron micrographs as seven to nine transverse stripes in the central portion of each half of the A band. Its C-terminus binds tightly to the myosin rod and contributes to thick filament structure, while the N-terminus can bind both myosin S2 and actin, influencing their structure and function. Mutations in the MYBPC3 gene (encoding cMyBP-C) are commonly associated with hypertrophic cardiomyopathy (HCM). In cardiac cells there exists a population of myosin heads in the super-relaxed (SRX) state, which are bound to the thick filament core with a highly inhibited ATPase activity. This report examines the role cMyBP-C plays in regulating the population of the SRX state of cardiac myosin by using an assay that measures single ATP turnover of myosin. We report a significant decrease in the proportion of myosin heads in the SRX state in homozygous cMyBP-C knockout mice, however heterozygous cMyBP-C knockout mice do not significantly differ from the wild type. A smaller, non-significant decrease is observed when thoracic aortic constriction is used to induce cardiac hypertrophy in mutation negative mice. These results support the proposal that cMyBP-C stabilises the thick filament and that the loss of cMyBP-C results in an untethering of myosin heads. This results in an increased myosin ATP turnover, further consolidating the relationship between thick filament structure and the myosin ATPase.
authors.affiliation: Discipline of Anatomy & Histology, Bosch Institute, University of Sydney, Sydney, NSW 2006, Australia. Electronic address: jmcn6970@uni.sydney.edu.au.
authors.forename: James W
authors.initials: JW
authors.lastname: McNamara
authors.affiliation: Discipline of Anatomy & Histology, Bosch Institute, University of Sydney, Sydney, NSW 2006, Australia.
authors.forename: Amy
authors.initials: A
authors.lastname: Li
authors.affiliation: Molecular Cardiology Program, Victor Chang Cardiac Research Institute, Darlinghurst, NSW 2010, Australia.
authors.forename: Nicola J
authors.initials: NJ
authors.lastname: Smith
authors.affiliation: Discipline of Anatomy & Histology, Bosch Institute, University of Sydney, Sydney, NSW 2006, Australia.
authors.forename: Sean
authors.initials: S
authors.lastname: Lal
authors.affiliation: Molecular Cardiology Program, Victor Chang Cardiac Research Institute, Darlinghurst, NSW 2010, Australia.
authors.forename: Robert M
authors.initials: RM
authors.lastname: Graham
authors.affiliation: Department of Pediatrics (Cardiology), Cardiovascular Institute, Stanford University, CA 94304, USA.
authors.forename: Kristina Bezold
authors.initials: KB
authors.lastname: Kooiker
authors.affiliation: Department of Cellular and Molecular Medicine, University of Arizona, Tucson, AZ 85721, USA.
authors.forename: Sabine J
authors.initials: SJ
authors.lastname: van Dijk
authors.affiliation: Discipline of Anatomy & Histology, Bosch Institute, University of Sydney, Sydney, NSW 2006, Australia.
authors.forename: Cristobal G Dos
authors.initials: CGD
authors.lastname: Remedios
authors.affiliation: Department of Cellular and Molecular Medicine, University of Arizona, Tucson, AZ 85721, USA.
authors.forename: Samantha P
authors.initials: SP
authors.lastname: Harris
authors.affiliation: Department of Biochemistry & Biophysics, Cardiovascular Research Institute, University of California, San Francisco, CA 94158-2517, USA.
authors.forename: Roger
authors.initials: R
authors.lastname: Cooke
mesh_terms: D000818:Animals; D024722:Cardiac Myosins / Q000378:metabolism*; D002312:Cardiomyopathy, Hypertrophic / Q000235:genetics / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D002352:Carrier Proteins / Q000235:genetics*; D005838:Genotype; D051379:Mice; D018345:Mice, Knockout; D032383:Myocytes, Cardiac / Q000378:metabolism*; D010766:Phosphorylation; D012518:Sarcomeres / Q000378:metabolism; D000099163:Myosin Binding Protein C
chemical_list: D024722:Cardiac Myosins; D002352:Carrier Proteins; D000099163:Myosin Binding Protein C
keywords: Cardiac SRX; Cardiac energetics; Hypertrophic cardiomyopathy; Myosin II ATPase; Myosin binding protein-C (MyBP-C); Thick filament structure