We propose a driving force hypothesis based on previous thermodynamics, kinetics and structural data as well as additional experiments and calculations presented here on water-related phenomena in the actomyosin systems. Although Szent-Györgyi pointed out the importance of water in muscle contraction in 1951, few studies have focused on the water science of muscle because of the difficulty of analyzing hydration properties of the muscle proteins, actin, and myosin. The thermodynamics and energetics of muscle contraction are linked to the water-mediated regulation of protein-ligand and protein-protein interactions along with structural changes in protein molecules. In this study, we assume the following two points: (1) the periodic electric field distribution along an actin filament (F-actin) is unidirectionally modified upon binding of myosin subfragment 1 (M or myosin S1) with ADP and inorganic phosphate Pi (M.ADP.Pi complex) and (2) the solvation free energy of myosin S1 depends on the external electric field strength and the solvation free energy of myosin S1 in close proximity to F-actin can become the potential force to drive myosin S1 along F-actin. The first assumption is supported by integration of experimental reports. The second assumption is supported by model calculations utilizing molecular dynamics (MD) simulation to determine solvation free energies of a small organic molecule and two small proteins. MD simulations utilize the energy representation method (ER) and the roughly proportional relationship between the solvation free energy and the solvent-accessible surface area (SASA) of the protein. The estimated driving force acting on myosin S1 is as high as several piconewtons (pN), which is consistent with the experimentally observed force.

Hydration state change of actin filament(F-actin) with bound myosin S1 after ATP hydrolysis were measured by precision microwave dielectric spectroscopy(DRS) at different molar ratio from 0:13 to 3:13 of S1:actin. In the previous study (BBRC 322(2004) [340][341][342][343][344][345][346], the hydration state of Factin with bound S1 exhibited a higher level of hypermobile water(HMW) number per actin than that of F-actin in spite of the absence of HMW around S1. Inthis study, with increasing the number of bound S1 on Factin, amount of HMW was found to increase non linearly, exhibiting a cooperative structural change in actin filament. 2P140ATP 結合アナログを用いたミオシンサブフラグメント１の 水和研究 Hydration study of myosin subflagment1 with bound ATP analogs Hideyuki Ohsugi, Takahiro Watanabe, Tetsuichi Wazawa, George Mogami, Makoto Suzuki (Grad. Sch. Eng., Tohoku Univ.)Hydration properties of myosin subfragment-1 (S1) with bound ADP.Pi analogs were measured by precision microwave dielectric spectroscopy (DRS). In the previous study (BJ, 72 (1997) 18-23), the intermediate state of S1 during ATP hydrolysis reaction, the mixed state of S1.ATP and S1.ADP.Pi, exhibited a lower level of hydration number, which was consistent with the thermodynamic parameter changes in entropy and heat capacity given by Kodama et al (Physiol. Rev. 65 (1985)467-551). However, in the present study, the hydration levels of S1.ADP.AlF4 and S1.ADP.Vi were higher than that of S1.ADP. It suggests that the S1 states with bound ADP.AlF4 and ADP.Vi are different from that in the dynamic ATP-hydrolysis cycle.2P141 2, 3-ブタンジオン 2-モノキシムによるミオシン II ATP 加水 分解のケミカルレスキュー BDM (2, 3-butandione 2-monoxime) is well characterized as an inhibitor of myosin motor. However, its inhibitory mechanism is not fully understood. We herein demonstrated that BDM elevates skeletal myosin II K + , EDTA-ATPase activity. In addition, BDM reactivates the ATPase activity of partially unfolded myosin. Furthermore, computational molecular modeling of docking of BDM on Dictyosteliummyosin IInucleotide complexes suggests two putative BDM-binding sites located around the the ATP site. Analogously to oxime compounds such as pralidoxime, which reactivate organophosphate-inactivated acetylcholinesterase, the oxime group of BDM may rescue the ATP hydrolysis of myosin. Based on these results, the mechanism of the inhibition of myosin motor will be discussed. 2P142F-アクチンの水和状態に及ぼす Mg2+と Ca2+の効果 Effect of Mg2+ and Ca2+ ions on the hydration state of F-actinRyotaro Chishima, Asato Imao, Takahiro Watanabe, Tetsuichi Wazawa, George Mogami, Makoto Suzuki (Grad. Sch. Eng., Tohoku Univ.)F-actin was reported to have dual hydration shell containing restrained water and hypermobile water (HMW) (BJ 85 (2003)3154-3161) and to exhibit marked increase in HMW upon binding mysion S1 by the previous study (BBRC 322(2004)340-346). In this study, hydration property of Factin was measured in two buffer solutions at 10C: (1) 2mM MgCl2, 50mM KCl, 10mM HEPES,1mM DTT, 0.1mM ATP at pH 7.8, (2) 2mM CaCl2, 50mM KCl, 10mM HEPES, 1mM DTT, 0...