title: Loop 1 dynamics in smooth muscle myosin: isoform specific differences modulate ADP release.
abstract: Isoforms of the smooth muscle (SM) myosin motor domain differ in the presence or absence of a seven amino acid insert in a flexible surface loop spanning the nucleotide-binding pocket known as Loop 1. The presence of this insert leads to a two-fold increase in actin sliding velocity and ADP release rate between these isoforms, although the effect of Loop 1 on the kinetics of ADP release remains unclear. To further investigate the role of the Loop 1 insert in modulating ADP release in SM myosin we have inserted a single tryptophan residue into Loop 1 of both isoforms as a probe of local structural dynamics. By monitoring the dynamics of Loop 1 in relation to the release of ADP we have observed a unique movement of Loop 1 in the inserted isoform, preceding nucleotide release, which is absent in the non-inserted isoform. This movement is sequence dependent as alanine replacement of the insert residues abolishes the transition and slows ADP release. Thus movement of Loop 1 is a critical factor in increasing the ADP release rate in the inserted faster isoform of SM myosin.
authors.affiliation: Department of Biochemistry, University of Vermont, College of Medicine, Burlington, VT, USA. jdecarre@uvm.edu
authors.forename: Justin A
authors.initials: JA
authors.lastname: Decarreau
authors.forename: Lynn R
authors.initials: LR
authors.lastname: Chrin
authors.forename: Christopher L
authors.initials: CL
authors.lastname: Berger
mesh_terms: D000199:Actins / Q000378:metabolism*; D000244:Adenosine Diphosphate / Q000378:metabolism; D000465:Algorithms; D000595:Amino Acid Sequence; D000818:Animals; D002645:Chickens; D031541:Fluorescence Resonance Energy Transfer / Q000379:methods; D007700:Kinetics; D008958:Models, Molecular; D009119:Muscle Contraction / Q000502:physiology; D009130:Muscle, Smooth / Q000378:metabolism*; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary; D011817:Rabbits; D011993:Recombinant Fusion Proteins; D024745:Smooth Muscle Myosins / Q000235:genetics / Q000378:metabolism
chemical_list: D000199:Actins; D020033:Protein Isoforms; D011993:Recombinant Fusion Proteins; D000244:Adenosine Diphosphate; D024745:Smooth Muscle Myosins