title: X-ray diffraction analysis of the effects of myosin regulatory light chain phosphorylation and butanedione monoxime on skinned skeletal muscle fibers.
abstract: The phosphorylation of the myosin regulatory light chain (RLC) is an important modulator of skeletal muscle performance and plays a key role in posttetanic potentiation and staircase potentiation of twitch contractions. The structural basis for these phenomena within the filament lattice has not been thoroughly investigated. Using a synchrotron radiation source at SPring8, we obtained X-ray diffraction patterns from skinned rabbit psoas muscle fibers before and after phosphorylation of myosin RLC in the presence of myosin light chain kinase, calmodulin, and calcium at a concentration below the threshold for tension development ([Ca(2+)] = 10(-6.8)M). After phosphorylation, the first myosin layer line slightly decreased in intensity at ∼0.05 nm(-1)along the equatorial axis, indicating a partial loss of the helical order of myosin heads along the thick filament. Concomitantly, the (1,1/1,0) intensity ratio of the equatorial reflections increased. These results provide a firm structural basis for the hypothesis that phosphorylation of myosin RLC caused the myosin heads to move away from the thick filaments towards the thin filaments, thereby enhancing the probability of interaction with actin. In contrast, 2,3-butanedione monoxime (BDM), known to inhibit contraction by impeding phosphate release from myosin, had exactly the opposite effects on meridional and equatorial reflections to those of phosphorylation. We hypothesize that these antagonistic effects are due to the acceleration of phosphate release from myosin by phosphorylation and its inhibition by BDM, the consequent shifts in crossbridge equilibria leading to opposite changes in abundance of the myosin-ADP-inorganic phosphate complex state associated with helical order of thick filaments.
authors.affiliation: Department of Molecular Physiology, The Jikei University School of Medicine, Tokyo, Japan; maki@jikei.ac.jp.
authors.forename: Maki
authors.initials: M
authors.lastname: Yamaguchi
authors.affiliation: Department of Molecular Physiology, The Jikei University School of Medicine, Tokyo, Japan;
authors.forename: Masako
authors.initials: M
authors.lastname: Kimura
authors.affiliation: Ludwig Center for Cancer Genetic and Therapeutics, The Johns Hopkins University, Baltimore, Maryland;
authors.forename: Zhao-Bo
authors.initials: ZB
authors.lastname: Li
authors.affiliation: Department of Molecular Physiology, The Jikei University School of Medicine, Tokyo, Japan;
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Ohno
authors.affiliation: Department of Molecular Physiology, The Jikei University School of Medicine, Tokyo, Japan;
authors.forename: Shigeru
authors.initials: S
authors.lastname: Takemori
authors.affiliation: Discipline of Physiology and the Bosch Institute, School of Medical Sciences, Sydney Medical School, The University of Sydney, New South Wales, Australia; and.
authors.forename: Joseph F Y
authors.initials: JF
authors.lastname: Hoh
authors.affiliation: Japan Synchrotron Radiation Research Institute, Hyogo, Japan.
authors.forename: Naoto
authors.initials: N
authors.lastname: Yagi
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D003931:Diacetyl / Q000031:analogs & derivatives* / Q000494:pharmacology; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure*; D018994:Myosin Light Chains / Q000502:physiology* / Q000648:ultrastructure*; D010766:Phosphorylation / Q000187:drug effects; D011817:Rabbits; D014961:X-Ray Diffraction / Q000379:methods
chemical_list: D018994:Myosin Light Chains; C004717:diacetylmonoxime; D003931:Diacetyl
keywords: X-ray diffraction; myosin regulatory light chain; phosphorylation; skinned fiber; twitch potentiation