title: Infrared spectroscopic studies on the V-ATPase.
abstract: V-ATPase is an ATP-driven rotary motor that vectorially transports ions. Together with F-ATPase, a homologous protein, several models on the ion transport have been proposed, but their molecular mechanisms are yet unknown. V-ATPase from Enterococcus hirae forms a large supramolecular protein complex (total molecular weight: ~700,000) and physiologically transports Na⁺ and Li⁺ across a hydrophobic lipid bilayer. Stabilization of these cations in the binding site has been discussed on the basis of X-ray crystal structures of a membrane-embedded domain, the K-ring (Na⁺ and Li⁺ bound forms). Sodium or lithium ion binding-induced difference FTIR spectra of the intact E. hirae V-ATPase have been measured in aqueous solution at physiological temperature. The results suggest that sodium or lithium ion binding induces the deprotonation of Glu139, a hydrogen-bonding change in the tyrosine residue and rigid α-helical structures. Identical difference FTIR spectra between the entire V-ATPase complex and K-ring strongly suggest that protein interaction with the I subunit does not cause large structural changes in the K-ring. This result supports the previously proposed Na⁺ transport mechanism by V-ATPase stating that a flip-flop movement of a carboxylate group of Glu139 without large conformational changes in the K-ring accelerates the replacement of a Na⁺ ion in the binding site. This article is part of a Special Issue entitled: Vibrational spectroscopies and bioenergetic systems.
authors.affiliation: Department of Frontier Materials, Nagoya Institute of Technology, Showa-ku, Nagoya 466-8555, Japan; OptoBioTechnology Research Center, Nagoya Institute of Technology, Showa-ku, Nagoya 466-8555, Japan. Electronic address: kandori@nitech.ac.jp.
authors.forename: Hideki
authors.initials: H
authors.lastname: Kandori
authors.affiliation: Department of Life and Coordination-Complex Molecular Science, Institute for Molecular Science, 38 Nishigo-Naka, Myodaiji, Okazaki 444-8585, Japan; Department of Structural Molecular Science, The Graduate University for Advanced Studies (SOKENDAI), 38 Nishigo-Naka, Myodaiji, Okazaki 444-8585, Japan.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Furutani
authors.affiliation: PRESTO, Japan Science and Technology Agency (JST), 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan; Department of Chemistry, Graduate School of Science, Chiba University, 1-33 Yayoi-cho, Inage, Chiba 263-8522, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Murata
mesh_terms: D001665:Binding Sites; D002414:Cations, Monovalent / Q000737:chemistry / Q000378:metabolism; D016983:Enterococcus / Q000737:chemistry / Q000378:metabolism; D006860:Hydrogen Bonding; D008094:Lithium / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D012964:Sodium / Q000737:chemistry / Q000378:metabolism; D013055:Spectrophotometry, Infrared / Q000379:methods; D025262:Vacuolar Proton-Translocating ATPases / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D002414:Cations, Monovalent; D008094:Lithium; D012964:Sodium; D025262:Vacuolar Proton-Translocating ATPases
keywords: ATR-FTIR spectroscopy; Conformation change; Protonation; Sodium binding; V(1)/V(o)-ATPase; X-ray crystallography