title: Three-dimensional structure of the myosin V inhibited state by cryoelectron tomography.
abstract: Unconventional myosin V (myoV) is an actin-based molecular motor that has a key function in organelle and mRNA transport, as well as in membrane trafficking. MyoV was the first member of the myosin superfamily shown to be processive, meaning that a single motor protein can 'walk' hand-over-hand along an actin filament for many steps before detaching. Full-length myoV has a low actin-activated MgATPase activity at low [Ca2+], whereas expressed constructs lacking the cargo-binding domain have a high activity regardless of [Ca2+] (refs 5-7). Hydrodynamic data and electron micrographs indicate that the active state is extended, whereas the inactive state is compact. Here we show the first three-dimensional structure of the myoV inactive state. Each myoV molecule consists of two heads that contain an amino-terminal motor domain followed by a lever arm that binds six calmodulins. The heads are followed by a coiled-coil dimerization domain (S2) and a carboxy-terminal globular cargo-binding domain. In the inactive structure, bending of myoV at the head-S2 junction places the cargo-binding domain near the motor domain's ATP-binding pocket, indicating that ATPase inhibition might occur through decreased rates of nucleotide exchange. The actin-binding interfaces are unobstructed, and the lever arm is oriented in a position typical of strong actin-binding states. This structure indicates that motor recycling after cargo delivery might occur through transport on actively treadmilling actin filaments rather than by diffusion.
authors.affiliation: The Institute of Molecular Biophysics, Florida State University, Tallahassee, Florida 32306-4380, USA.
authors.forename: Jun
authors.initials: J
authors.lastname: Liu
authors.forename: Dianne W
authors.initials: DW
authors.lastname: Taylor
authors.forename: Elena B
authors.initials: EB
authors.lastname: Krementsova
authors.forename: Kathleen M
authors.initials: KM
authors.lastname: Trybus
authors.forename: Kenneth A
authors.initials: KA
authors.lastname: Taylor
mesh_terms: D000199:Actins / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure; D000818:Animals; D020285:Cryoelectron Microscopy; D004058:Diffusion; D051379:Mice; D008958:Models, Molecular; D024701:Myosin Type V / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000648:ultrastructure*; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary
chemical_list: D000199:Actins; D024701:Myosin Type V