1998 Fiscal Year Final Research Report Summary
Fluctuation analysis of actin in vitro sliding along native thick filaments from molluscan smooth muscles
| Project/Area Number |
09480178
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Biophysics
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| Research Institution | KYUSHU UNIVERSITY |
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Principal Investigator |
TAWADA Katsuhisa Kyushu Univ., Faculty of Science, Professor, 理学部, 教授 (20029507)
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| Co-Investigator(Kenkyū-buntansha) |
YAMADA Akira Communication Research Laboratory, Kansai Advanced Research Center, Senior Resea, 通信総合研究所関西支所, 主任研究員
SEKIMOTO Ken Kyoto Univ., Yukawa Institute for Theoretical Physics, Professor, 基礎物理学研究所, 教授 (00179342)
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| Project Period (FY) |
1997 – 1998
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| Keywords | protein motors / myosin / actin / sliding movement / sliding distance / fluctuation analysis / central limit theorem |
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| Research Abstract |
1) We purified long myosin thick filaments from molluscan smooth muscles, in which myosin motors are well oriented, and we recorded sliding movements of many actin filaments with various lengths along individual myosin thick filaments in vitro. We obtained good recordings with five different myosin thick filaments.
2) We analyzed the fluctuation of the sliding distance of actin filaments, by calculating the variance of the sliding distance for a given period of time. The analysis yields a value of an effective diffusion coefficient, Din, for each actin filament. We then studied dependence of Dm on the actin filament length, and found that Dm does not depend on the actin length and is constant, as was previously found with randomly oriented motor proteins in vitro.
3) It is often believed that the actions of motor proteins in driving a cytoskeletal filament to slide unidirectionally are statistically independent and random. If this is the case, we can expect that Dm is proportional to the inverse of the actin filament length, which is a direct consequence of the central limit theorem. By computer simulation with Huxley's 1957 model of 'spring myosins' we confirmed this theoretical prediction that the fluctuation of sliding distance is proportional to the inverse of the filament length if the motor actions are random and statistically independent.
4) However, the above experimental finding that Din does not depend on the actin filament length indicates that this belief does not hold in the case of the in vitro sliding movement generation by protein motors, and instead indicates that there is a cooperativity in the mechanism of the directional sliding movement generation by motor proteins.
5) We therefore conclude that the actions of myosin motors in generating the unidirectional sliding movement of actin filaments are not random and there must be cooperativity in their actions. We are currently studying possible mechanisms of the cooperativity by computer simulation.
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