title: Dynamic structures of motor proteins myosin and kinesin, and switch protein troponin as detected by SDSL-ESR.
abstract: We have studied biological nano-machines, motor and switch proteins operating as supramolecular complexes by electron spin resonance (ESR) and found key features of their molecular movements. In all the systems, the specific movements of elements or domains were detected and quite dynamic at nanometer scale. We have observed two broad but distinct orientations, separated by a 25 degrees axial rotation, of a spin label attached specifically to the light chain (LC) domain of myosin motor in the muscle fibers. The distribution became only narrower upon muscle activation. ESR spectrum from the spin label of the neck-linker of dimeric kinesin motor consisted of immobilized and mobilized components and did not exhibit nucleotide-dependent mobility change. The distance between two labels of kinesin dimer was also measured by spin dipole-dipole interaction, showing a broad distribution and a nucleotide-dependent change on the nanometer scale (>1.5 nm). These results suggest that two LC domains of myosin and two neck linkers of kinesin play a similar role for sliding movement using two conformations. The spin label of the skeletal (Tn)-I regulatory domain (TnIreg) showed a large mobility change by Ca2+ ion suggesting a Ca-induced switch movement of TnIreg. Spin dipole-dipole interaction showed that in reconstituted muscle fibers both skeletal and cardiac TnC undergo Ca2+-induced structural change that is thought to be essential for TnIreg movement. We also succeeded in fixing the newly-synthesized bifunctional spin label rigidly on the TnC molecule in solution, indicating that we can determine the precise coordinate of the spin principal axis of troponin on the oriented filament.
authors.affiliation: Department of Biology, Graduate School of Science, Osaka University, 1-1 Machikeneyama-cho, Toyonaka 560-0043, Japan. arata@bio.sci.osaka-u.ac.jp
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Arata
authors.forename: Motoyoshi
authors.initials: M
authors.lastname: Nakamura
authors.forename: Shoji
authors.initials: S
authors.lastname: Ueki
authors.forename: Kazunori
authors.initials: K
authors.lastname: Sugata
authors.forename: Tomoki
authors.initials: T
authors.lastname: Aihara
authors.forename: Keisuke
authors.initials: K
authors.lastname: Ueda
authors.forename: Satoshi
authors.initials: S
authors.lastname: Yasuda
authors.forename: Ryouhei
authors.initials: R
authors.lastname: Narumi
authors.forename: Hiroko
authors.initials: H
authors.lastname: Kusuhara
authors.forename: Yukio
authors.initials: Y
authors.lastname: Yamamoto
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D006801:Humans; D016547:Kinesins / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D009119:Muscle Contraction; D018485:Muscle Fibers, Skeletal; D009126:Muscle Relaxation; D018482:Muscle, Skeletal; D018994:Myosin Light Chains / Q000737:chemistry / Q000378:metabolism; D016658:Psoas Muscles; D011817:Rabbits; D013113:Spin Labels; D014336:Troponin / Q000737:chemistry / Q000378:metabolism; D019209:Troponin C / Q000737:chemistry / Q000378:metabolism; D019210:Troponin I / Q000737:chemistry / Q000378:metabolism
chemical_list: D018994:Myosin Light Chains; D013113:Spin Labels; D014336:Troponin; D019209:Troponin C; D019210:Troponin I; D016547:Kinesins; D002118:Calcium