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Journal of Electron Microscopy 2005 54(supplement 1):i47-i51; doi:10.1093/jmicro/54.suppl_1.i47
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© The Author 2005. Published by Oxford University Press on behalf of Japanese Society of Microscopy. All rights reserved. For permissions, please email: journals.permissions@oupjournals.org

Article

Dynamic structures of motor proteins myosin and kinesin, and switch protein troponin as detected by SDSL-ESR

Toshiaki Arata1,2,*, Motoyoshi Nakamura1, Shoji Ueki1,2, Kazunori Sugata1, Tomoki Aihara1, Keisuke Ueda1, Satoshi Yasuda1, Ryouhei Narumi1, Hiroko Kusuhara1 and Yukio Yamamoto3

1 Department of Biology, Graduate School of Science, Osaka University and 2 CREST/JST, 1-1 Machikeneyama-cho, Toyonaka 560-0043 and 3 Graduate School of Human and Environmental Studies, Kyoto University, Yoshida-nihonmatsu-cho, Sakyo-ku, Kyoto 606-8501, Japan

* To whom correspondence should be addressed. E-mail: arata{at}bio.sci.osaka-u.ac.jp

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° 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.

Keywords     bionanomachine, kinesin, myosin, troponin, electron magnetic resonance, spin label

Received     27 July 2004, accepted 15 October 2004


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