title: A mutant heterodimeric myosin with one inactive head generates maximal displacement.
abstract: Each of the heads of the motor protein myosin II is capable of supporting motion. A previous report showed that double-headed myosin generates twice the displacement of single-headed myosin (Tyska, M.J., D.E. Dupuis, W.H. Guilford, J.B. Patlak, G.S. Waller, K.M. Trybus, D.M. Warshaw, and S. Lowey. 1999. Proc. Natl. Acad. Sci. USA. 96:4402-4407). To determine the role of the second head, we expressed a smooth muscle heterodimeric heavy meromyosin (HMM) with one wild-type head, and the other locked in a weak actin-binding state by introducing a point mutation in switch II (E470A). Homodimeric E470A HMM did not support in vitro motility, and only slowly hydrolyzed MgATP. Optical trap measurements revealed that the heterodimer generated unitary displacements of 10.4 nm, strikingly similar to wild-type HMM (10.2 nm) and approximately twice that of single-headed subfragment-1 (4.4 nm). These data show that a double-headed molecule can achieve a working stroke of approximately 10 nm with only one active head and an inactive weak-binding partner. We propose that the second head optimizes the orientation and/or stabilizes the structure of the motion-generating head, thereby resulting in maximum displacement.
authors.affiliation: Department of Molecular Physiology and Biophysics, University of Vermont, Health Science Research Facility, Burlington, VT 05405-0068, USA.
authors.forename: Neil M
authors.initials: NM
authors.lastname: Kad
authors.forename: Arthur S
authors.initials: AS
authors.lastname: Rovner
authors.forename: Patricia M
authors.initials: PM
authors.lastname: Fagnant
authors.forename: Peteranne B
authors.initials: PB
authors.lastname: Joel
authors.forename: Guy G
authors.initials: GG
authors.lastname: Kennedy
authors.forename: Joseph B
authors.initials: JB
authors.lastname: Patlak
authors.forename: David M
authors.initials: DM
authors.lastname: Warshaw
authors.forename: Kathleen M
authors.initials: KM
authors.lastname: Trybus
mesh_terms: D000199:Actins / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001665:Binding Sites / Q000235:genetics; D002460:Cell Line; D002465:Cell Movement / Q000235:genetics*; D019281:Dimerization; D005057:Eukaryotic Cells / Q000378:metabolism*; D009154:Mutation / Q000235:genetics; D009218:Myosins / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary / Q000235:genetics
chemical_list: D000199:Actins; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D009218:Myosins