title: Differential labeling of myosin V heads with quantum dots allows direct visualization of hand-over-hand processivity.
abstract: The double-headed myosin V molecular motor carries intracellular cargo processively along actin tracks in a hand-over-hand manner. To test this hypothesis at the molecular level, we observed single myosin V molecules that were differentially labeled with quantum dots having different emission spectra so that the position of each head could be identified with approximately 6-nm resolution in a total internal reflectance microscope. With this approach, the individual heads of a single myosin V molecule were observed taking 72-nm steps as they alternated positions on the actin filament during processive movement. In addition, the heads were separated by 36 nm during pauses in motion, suggesting attachment to actin along its helical repeat. The 36-nm interhead spacing, the 72-nm step size, and the observation that heads alternate between leading and trailing positions on actin are obvious predictions of the hand-over-hand model, thus confirming myosin V's mode of walking along an actin filament.
authors.affiliation: Department of Molecular Physiology & Biophysics, University of Vermont, Burlington, Vermont 05405, USA. warshaw@physiology.med.uvm.edu
authors.forename: David M
authors.initials: DM
authors.lastname: Warshaw
authors.forename: Guy G
authors.initials: GG
authors.lastname: Kennedy
authors.forename: Steven S
authors.initials: SS
authors.lastname: Work
authors.forename: Elena B
authors.initials: EB
authors.lastname: Krementsova
authors.forename: Samantha
authors.initials: S
authors.lastname: Beck
authors.forename: Kathleen M
authors.initials: KM
authors.lastname: Trybus
mesh_terms: D000199:Actins / Q000737:chemistry; D001426:Bacterial Proteins / Q000737:chemistry; D001665:Binding Sites; D001703:Biophysics / Q000379:methods*; D001710:Biotin / Q000737:chemistry; D007834:Lasers; D008164:Luminescent Proteins / Q000737:chemistry; D008857:Microscopy, Interference / Q000379:methods; D015879:Myosin Subfragments / Q000737:chemistry; D024701:Myosin Type V / Q000737:chemistry*; D016011:Normal Distribution; D045663:Quantum Dots; D013053:Spectrophotometry; D013997:Time Factors
chemical_list: D000199:Actins; D001426:Bacterial Proteins; D008164:Luminescent Proteins; D015879:Myosin Subfragments; C054562:yellow fluorescent protein, Bacteria; D001710:Biotin; D024701:Myosin Type V