Fluid Mechanical Matching of H-ATP Synthase Subunit c-Ring with Lipid Membranes Revealed by H Solid-State NMR |
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Authors: | Masatoshi Kobayashi Andrey V Struts Michael F Brown Hideo Akutsu |
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Institution: | * Institute for Protein Research, Osaka University, Yamadoaka, Suita 565-0871, Japan † Department of Chemistry, University of Arizona, Tucson, Arizona 85721 ‡ Department of Physics, University of Arizona, Tucson, Arizona 85721 § Core Research of Evolutional Science and Technology, Japan Science and Technology Agency, Japan |
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Abstract: | The F1Fo-ATP synthase utilizes the transmembrane H+ gradient for the synthesis of ATP. Fo subunit c-ring plays a key role in transporting H+ through Fo in the membrane. We investigated the interactions of Escherichia coli subunit c with dimyristoylphosphatidylcholine (DMPC-d54) at lipid/protein ratios of 50:1 and 20:1 by means of 2H-solid-state NMR. In the liquid-crystalline state of DMPC, the 2H-NMR moment values and the order parameter (SCD) profile were little affected by the presence of subunit c, suggesting that the bilayer thickness in the liquid-crystalline state is matched to the transmembrane hydrophobic surface of subunit c. On the other hand, hydrophobic mismatch of subunit c with the lipid bilayer was observed in the gel state of DMPC. Moreover, the viscoelasticity represented by a square-law function of the 2H-NMR relaxation was also little influenced by subunit c in the fluid phase, in contrast with flexible nonionic detergents or rigid additives. Thus, the hydrophobic matching of the lipid bilayer to subunit c involves at least two factors, the hydrophobic length and the fluid mechanical property. These findings may be important for the torque generation in the rotary catalytic mechanism of the F1Fo-ATPse molecular motor. |
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