title: Analysis of myosin heavy chain functionality in the heart.
abstract: Comparison of mammalian cardiac alpha- and beta-myosin heavy chain isoforms reveals 93% identity. To date, genetic methodologies have effected only minor switches in the mammalian cardiac myosin isoforms. Using cardiac-specific transgenesis, we have now obtained major myosin isoform shifts and/or replacements. Clusters of non-identical amino acids are found in functionally important regions, i.e. the surface loops 1 and 2, suggesting that these structures may regulate isoform-specific characteristics. Loop 1 alters filament sliding velocity, whereas Loop 2 modulates actin-activated ATPase rate in Dictyostelium myosin, but this remains untested in mammalian cardiac myosins. Alpha --> beta isoform switches were engineered into mouse hearts via transgenesis. To assess the structural basis of isoform diversity, chimeric myosins in which the sequences of either Loop 1+Loop 2 or Loop 2 of alpha-myosin were exchanged for those of beta-myosin were expressed in vivo. 2-fold differences in filament sliding velocity and ATPase activity were found between the two isoforms. Filament sliding velocity of the Loop 1+Loop 2 chimera and the ATPase activities of both loop chimeras were not significantly different compared with alpha-myosin. In mouse cardiac isoforms, myosin functionality does not depend on Loop 1 or Loop 2 sequences and must lie partially in other non-homologous residues.
authors.affiliation: Cincinnati Children's Hospital Medical Center, The Children's Hospital Research Foundation, MLC 7020, Cincinnati, Ohio 45229-3039, USA.
authors.forename: Maike
authors.initials: M
authors.lastname: Krenz
authors.forename: Atsushi
authors.initials: A
authors.lastname: Sanbe
authors.forename: Florence
authors.initials: F
authors.lastname: Bouyer-Dalloz
authors.forename: James
authors.initials: J
authors.lastname: Gulick
authors.forename: Raisa
authors.initials: R
authors.lastname: Klevitsky
authors.forename: Timothy E
authors.initials: TE
authors.lastname: Hewett
authors.forename: Hanna E
authors.initials: HE
authors.lastname: Osinska
authors.forename: John N
authors.initials: JN
authors.lastname: Lorenz
authors.forename: Christine
authors.initials: C
authors.lastname: Brosseau
authors.forename: Andrea
authors.initials: A
authors.lastname: Federico
authors.forename: Norman R
authors.initials: NR
authors.lastname: Alpert
authors.forename: David M
authors.initials: DM
authors.lastname: Warshaw
authors.forename: M Benjamin
authors.initials: MB
authors.lastname: Perryman
authors.forename: Steve M
authors.initials: SM
authors.lastname: Helmke
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Robbins
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D006321:Heart / Q000502:physiology*; D051379:Mice; D008822:Mice, Transgenic; D008969:Molecular Sequence Data; D009206:Myocardium / Q000378:metabolism; D018995:Myosin Heavy Chains / Q000502:physiology*; D020033:Protein Isoforms / Q000502:physiology; D011993:Recombinant Fusion Proteins / Q000502:physiology
chemical_list: D020033:Protein Isoforms; D011993:Recombinant Fusion Proteins; D018995:Myosin Heavy Chains; D000252:Calcium-Transporting ATPases; D002118:Calcium