title: Myosin VI steps via a hand-over-hand mechanism with its lever arm undergoing fluctuations when attached to actin.
abstract: Myosin VI is a reverse direction myosin motor that, as a dimer, moves processively on actin with an average center-of-mass movement of approximately 30 nm for each step. We labeled myosin VI with a single fluorophore on either its motor domain or on the distal of two calmodulins (CaMs) located on its putative lever arm. Using a technique called FIONA (fluorescence imaging with one nanometer accuracy), step size was observed with a standard deviation of <1.5 nm, with 0.5-s temporal resolution, and observation times of minutes. Irrespective of probe position, the average step size of a labeled head was approximately 60 nm, strongly supporting a hand-over-hand model of motility and ruling out models in which the unique myosin VI insert comes apart. However, the CaM probe displayed large spatial fluctuations (presence of ATP but not ADP or no nucleotide) around the mean position, whereas the motor domain probe did not. This supports a model of myosin VI motility in which the lever arm is either mechanically uncoupled from the motor domain or is undergoing reversible isomerization for part of its motile cycle on actin.
authors.affiliation: Center for Biophysics and Computational Biology, Loomis Laboratory, University of Illinois, Urbana, Illinois 61801, USA.
authors.forename: Ahmet
authors.initials: A
authors.lastname: Yildiz
authors.forename: Hyokeun
authors.initials: H
authors.lastname: Park
authors.forename: Dan
authors.initials: D
authors.lastname: Safer
authors.forename: Zhaohui
authors.initials: Z
authors.lastname: Yang
authors.forename: Li-Qiong
authors.initials: LQ
authors.lastname: Chen
authors.forename: Paul R
authors.initials: PR
authors.lastname: Selvin
authors.forename: H Lee
authors.initials: HL
authors.lastname: Sweeney
mesh_terms: D000199:Actins / Q000378:metabolism*; D000595:Amino Acid Sequence; D005453:Fluorescence; D018995:Myosin Heavy Chains / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding
chemical_list: D000199:Actins; C089785:myosin VI; D018995:Myosin Heavy Chains