title: Structure of myosin filaments from relaxedLethocerusflight muscle by cryo-EM at 6 Å resolution.
abstract: We describe a cryo-electron microscopy three-dimensional image reconstruction of relaxed myosin II-containing thick filaments from the flight muscle of the giant water bugLethocerus indicus. The relaxed thick filament structure is a key element of muscle physiology because it facilitates the reextension process following contraction. Conversely, the myosin heads must disrupt their relaxed arrangement to drive contraction. Previous models predicted thatLethocerusmyosin was unique in having an intermolecular head-head interaction, as opposed to the intramolecular head-head interaction observed in all other species. In contrast to the predicted model, we find an intramolecular head-head interaction, which is similar to that of other thick filaments but oriented in a distinctly different way. The arrangement of myosin's long α-helical coiled-coil rod domain has been hypothesized as either curved layers or helical subfilaments. Our reconstruction is the first report having sufficient resolution to track the rod α helices in their native environment at resolutions ~5.5 Å, and it shows that the layer arrangement is correct forLethocerus. Threading separate paths through the forest of myosin coiled coils are four nonmyosin peptides. We suggest that the unusual position of the heads and the rod arrangement separated by nonmyosin peptides are adaptations for mechanical signal transduction whereby applied tension disrupts the myosin heads as a component of stretch activation.
authors.affiliation: Institute of Molecular Biophysics, Florida State University, Tallahassee, FL 32306-4380, USA.
authors.forename: Zhongjun
authors.initials: Z
authors.lastname: Hu
authors.affiliation: Institute of Molecular Biophysics, Florida State University, Tallahassee, FL 32306-4380, USA.
authors.forename: Dianne W
authors.initials: DW
authors.lastname: Taylor
authors.affiliation: Department of Cell Biology, Duke University Medical Center, Durham, NC 27607, USA.
authors.forename: Michael K
authors.initials: MK
authors.lastname: Reedy
authors.affiliation: Department of Cell Biology, Duke University Medical Center, Durham, NC 27607, USA.
authors.forename: Robert J
authors.identifier: 0000-0003-4446-1194
authors.initials: RJ
authors.lastname: Edwards
authors.affiliation: Institute of Molecular Biophysics, Florida State University, Tallahassee, FL 32306-4380, USA.
authors.forename: Kenneth A
authors.identifier: 0000-0001-9594-8360
authors.initials: KA
authors.lastname: Taylor
mesh_terms: D008841:Actin Cytoskeleton / Q000648:ultrastructure; D000818:Animals; D020285:Cryoelectron Microscopy / Q000379:methods*; D003599:Cytoskeleton / Q000648:ultrastructure*; D005426:Flight, Animal / Q000502:physiology; D020062:Heteroptera / Q000648:ultrastructure; D021621:Imaging, Three-Dimensional / Q000379:methods; D008958:Models, Molecular; D009119:Muscle Contraction / Q000502:physiology; D009132:Muscles / Q000502:physiology / Q000648:ultrastructure*; D009218:Myosins / Q000648:ultrastructure*
chemical_list: D009218:Myosins
keywords: IHRSR; Muscle fiber; electron microscopy; fibrillar muscle; flightin; image processing; myofilin; paramyosin; stretch activation