title: Human homozygous R403W mutant cardiac myosin presents disproportionate enhancement of mechanical and enzymatic properties.
abstract: Familial hypertrophic cardiomyopathy (FHC) is associated with mutations in 11 genes encoding sarcomeric proteins. Most families present mutations in MYBPC3 and MYH7 encoding cardiac myosin-binding protein C and beta-myosin heavy chain. The consequences of MYH7 mutations have been extensively studied at the molecular level, but controversial results have been obtained with either reduced or augmented myosin motor function depending on the type or homogeneity of myosin studied. In the present study, we took advantage of the accessibility to an explanted heart to analyze for the first time the properties of human homozygous mutant myosin. The patient exhibited eccentric hypertrophy with severely impaired ejection fraction leading to heart transplantation, and carries a homozygous mutation in MYH7 (R403W) and a heterozygous variant in MYBPC3 (V896M). In situ analysis of the left ventricular tissue showed myocyte disarray and hypertrophy plus interstitial fibrosis. In vitro motility assays showed a small, but significant increase in sliding velocity of fluorescent-labeled actin filaments over human mutant cardiac myosin-coated surface compared to control (+18%; P<0.001). Mutant myosin exhibited a large increase in maximal actin-activated ATPase activity (+114%; P<0.05) and Km for actin (+87%; P<0.05) when compared to control. These data show disproportionate enhancement of mechanical and enzymatic properties of human mutant myosin. This suggests inefficient ATP utilization and reduced mechanical efficiency in the myocardial tissue of the patient, which could play an important role in the development of FHC phenotype.
authors.affiliation: INSERM U582, Institut de Myologie, Bâtiment Babinski, Groupe Hospitalier Pitié-Salpêtrière, 47, Bld de l'Hôpital, 75651 Paris cedex 13, France.
authors.forename: Dagmar I
authors.initials: DI
authors.lastname: Keller
authors.forename: Catherine
authors.initials: C
authors.lastname: Coirault
authors.forename: Thomas
authors.initials: T
authors.lastname: Rau
authors.forename: Theary
authors.initials: T
authors.lastname: Cheav
authors.forename: Michael
authors.initials: M
authors.lastname: Weyand
authors.forename: Kerstin
authors.initials: K
authors.lastname: Amann
authors.forename: Yves
authors.initials: Y
authors.lastname: Lecarpentier
authors.forename: Pascale
authors.initials: P
authors.lastname: Richard
authors.forename: Thomas
authors.initials: T
authors.lastname: Eschenhagen
authors.forename: Lucie
authors.initials: L
authors.lastname: Carrier
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000737:chemistry*; D000255:Adenosine Triphosphate / Q000378:metabolism; D000293:Adolescent; D000328:Adult; D000818:Animals; D001483:Base Sequence; D024741:Cardiomyopathy, Hypertrophic, Familial / Q000201:enzymology / Q000235:genetics* / Q000473:pathology; D002352:Carrier Proteins / Q000235:genetics*; D006801:Humans; D020409:Molecular Motor Proteins / Q000235:genetics; D008969:Molecular Sequence Data; D018995:Myosin Heavy Chains / Q000737:chemistry / Q000235:genetics*; D017354:Point Mutation / Q000235:genetics; D011817:Rabbits; D017422:Sequence Analysis, DNA; D000099163:Myosin Binding Protein C
chemical_list: D000251:Adenosine Triphosphatases; D000255:Adenosine Triphosphate; D002352:Carrier Proteins; D020409:Molecular Motor Proteins; D018995:Myosin Heavy Chains; D000099163:Myosin Binding Protein C