8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

P4.66Fri 911:10-14:00On the physical mechanism of rotation of F1-ATPase:crucial importance of the water entropy effectTakashi Yoshidome, 1 Yuko Ito, 1 Mitsunori Ikeguchi, 2 and Masahiro Kinoshita 11 Institute of Advanced Energy, Kyoto University, Gokasho, 611-0011, Uji, Japan2 Graduate School of Nanobioscience, Yokohama City University, Yokohama, JapanWe propose a novel picture of the rotation mechanism of F1-ATPase [1] whose minimum complexneeded for the rotation is composed of the three alpha subunits, the three beta subunits, and thegamma subunit. In the proposal, the key factor is the translational entropy of water, which hasbeen shown to drive a variety of self-assembly processes in biological systems [2]. We calculatethe water-entropy gains upon formation of the alpha-beta, alpha-gamma, and beta-gamma subunitpairs. The gain is given as the difference between the hydration entropy of a subunit pair and thesum of the hydration entropies of the separate subunits forming the pair. The calculation is madeusing the angle-dependent integral equation theory combined with the multipolar water model [3]and morphometric approach [4]. The water-entropy gain is considered as a measure of tightnessof the packing at each subunit interface. The results are highly correlated with the numbers ofstable contacts at the subunit interfaces estimated by an all-atom molecular dynamics simulation[5]. We also calculate the hydration entropies of three different sub-complexes comprising thegamma subunit, one of the beta subunits, and two alpha subunits adjacent to them. The majorfinding is that the packing in F1-ATPase is highly asymmetrical and this asymmetry is ascribedto the water-entropy effect. We discuss how the rotation of the gamma subunit is induced bysuch chemical processes as ATP binding, ATP hydrolysis, and release of the products. In ourpicture, the asymmetrical packing plays crucially important roles and the rotation is driven by thewater-entropy effect.[1] T. Yoshidome, Y. Ito, M. Ikeguchi, and M. Kinoshita, J. Am. Chem. Soc. 133, 4030(2011).[2] M. Kinoshita, Front. Biosci. 14, 3419 (2009).[3] M. Kinoshita, J. Chem. Phys. 128, 024507 (2008).[4] R. Roth, Y. Harano, and M. Kinoshita, Phys. Rev. Lett. 97, 078101 (2006).[5] Y. Ito and M. Ikeguchi, J. Comp. Chem. 31, 2175 (2010).66