Hyper-mobility of water around actin filaments revealed using pulse-field gradient spin-echo H NMR and fluorescence spectroscopy |
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Authors: | Tetsuichi Wazawa Takashi Sagawa Tsubasa Ogawa Nobuyuki Morimoto Takao Kodama Makoto Suzuki |
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Institution: | aDepartment of Materials Processing, Graduate School of Tohoku University, 6-6-02 Aobayama, Aoba-Ku, Sendai, Miyagi 980-8579, Japan;bCREST, JST, 4-1-8, Honcho, Kawaguchi, Saitama 332-0012, Japan;cImmunology Frontier Research Center, Osaka University, 3-1 Yamada-Oka, Suita, Osaka 565-0871, Japan |
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Abstract: | This paper reports that water molecules around F-actin, a polymerized form of actin, are more mobile than those around G-actin or in bulk water. A measurement using pulse-field gradient spin-echo 1H NMR showed that the self-diffusion coefficient of water in aqueous F-actin solution increased with actin concentration by ∼5%, whereas that in G-actin solution was close to that of pure water. This indicates that an F-actin/water interaction is responsible for the high self-diffusion of water. The local viscosity around actin was also investigated by fluorescence measurements of Cy3, a fluorescent dye, conjugated to Cys 374 of actin. The steady-state fluorescence anisotropy of Cy3 attached to F-actin was 0.270, which was lower than that for G-actin, 0.334. Taking into account the fluorescence lifetimes of the Cy3 bound to actin, their rotational correlation times were estimated to be 3.8 and 9.1 ns for F- and G-actin, respectively. This indicates that Cy3 bound to F-actin rotates more freely than that bound to G-actin, and therefore the local water viscosity is lower around F-actin than around G-actin. |
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Keywords: | Self-diffusion Fluorescence anisotropy Rotational correlation time Local viscosity Structure-breaker Hyper-mobile water Endothermic process Actin polymerization |
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