title: Dynamics of actomyosin interactions in relation to the cross-bridge cycle.
abstract: Transient kinetic measurements of the actomyosin ATPase provided the basis of the Lymn-Taylor model for the cross-bridge cycle, which underpins current models of contraction. Following the determination of the structure of the myosin motor domain, it has been possible to introduce probes at defined sites and resolve the steps in more detail. Probes have been introduced in the Dicytostelium myosin II motor domain via three routes: (i) single tryptophan residues at strategic locations throughout the motor domain; (ii) green fluorescent protein fusions at the N and C termini; and (iii) labelled cysteine residues engineered across the actin-binding cleft. These studies are interpreted with reference to motor domain crystal structures and suggest that the tryptophan (W501) in the relay loop senses the lever arm position, which is controlled by the switch 2 open-to-closed transition at the active site. Actin has little effect on this process per se. A mechanism of product release is proposed in which actin has an indirect effect on the switch 2 and lever arm position to achieve mechanochemical coupling. Switch 1 closing appears to be a key step in the nucleotide-induced actin dissociation, while its opening is required for the subsequent activation of product release. This process has been probed with F239W and F242W substitutions in the switch 1 loop. The E706K mutation in skeletal myosin IIa is associated with a human myopathy. To simulate this disease we investigated the homologous mutation, E683K, in the Dictyostelium myosin motor domain.
authors.affiliation: Department of Biochemistry, University of Leicester, Leicester LE1 7RH, UK.
authors.forename: Wei
authors.initials: W
authors.lastname: Zeng
authors.forename: Paul B
authors.initials: PB
authors.lastname: Conibear
authors.forename: Jane L
authors.initials: JL
authors.lastname: Dickens
authors.forename: Ruth A
authors.initials: RA
authors.lastname: Cowie
authors.forename: Stuart
authors.initials: S
authors.lastname: Wakelin
authors.forename: András
authors.initials: A
authors.lastname: Málnási-Csizmadia
authors.forename: Clive R
authors.initials: CR
authors.lastname: Bagshaw
mesh_terms: D000199:Actins / Q000378:metabolism / Q000502:physiology*; D000818:Animals; D001665:Binding Sites; D001696:Biomechanical Phenomena; D004023:Dictyostelium; D007700:Kinetics; D008958:Models, Molecular; D020409:Molecular Motor Proteins / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology*; D009132:Muscles / Q000502:physiology*; D009154:Mutation / Q000235:genetics; D009218:Myosins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D011487:Protein Conformation; D014364:Tryptophan / Q000378:metabolism* / Q000502:physiology
chemical_list: D000199:Actins; D020409:Molecular Motor Proteins; D014364:Tryptophan; D009218:Myosins