title: The Role of the NDQ Motif in Sodium-Pumping Rhodopsins.
abstract: Sodium-pumping rhodopsins (NaRs) are light-driven outward Na(+) pumps. NaRs have a conserved Asn, Asp, and Gln motif (NDQ) in the third transmembrane helix (helix C). The NDQ motif is thus expected to play a crucial role in the operation of the Na(+) pump. Herein, we studied the photocycles of the NDQ-motif mutants of Krokinobacter rhodopsin 2 (KR2), the first discovered NaR, by flash photolysis, to obtain insight into the mechanism of Na(+) transport. For example, the KR2 N112A mutant did not accumulate the transient red-shifted Na(+)-bound state, suggesting that Asn112 is vital for the binding of Na(+) ions. Additionally, Q123A and Q123V mutants showed significantly slower Na(+) uptake and recovery of the initial state. Overall, the Gln123 residue was found to contribute to the optimization of the kinetics of sodium-ion uptake and release. These results demonstrate that the cooperative operation of the three residues of the NDQ motif are important in the operation of the Na(+) pump.
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).|PRESTO, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012 (Japan).
authors.forename: Keiichi
authors.initials: K
authors.lastname: Inoue
authors.affiliation: Department of Frontier Materials, Nagoya Institute of Technology, Showa-ku, Nagoya 466-8555 (Japan).
authors.forename: Masae
authors.initials: M
authors.lastname: Konno
authors.affiliation: Department of Frontier Materials, Nagoya Institute of Technology, Showa-ku, Nagoya 466-8555 (Japan).
authors.forename: Rei
authors.initials: R
authors.lastname: Abe-Yoshizumi
authors.affiliation: Department of Frontier Materials, Nagoya Institute of Technology, Showa-ku, Nagoya 466-8555 (Japan). kandori@nitech.ac.jp.|OptoBioTechnology Research Center, Nagoya Institute of Technology, Showa-ku, Nagoya 466-8555 (Japan). kandori@nitech.ac.jp.
authors.forename: Hideki
authors.initials: H
authors.lastname: Kandori
mesh_terms: D020816:Amino Acid Motifs; D001692:Biological Transport; D041965:Flavobacteriaceae / Q000737:chemistry*; D012243:Rhodopsin / Q000737:chemistry / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D013053:Spectrophotometry
chemical_list: D012243:Rhodopsin; D012964:Sodium
keywords: kinetics; photolysis; proteins; rhodopsin; sodium pump