title: Mutant of a Light-Driven Sodium Ion Pump Can Transport Cesium Ions.
abstract: Krokinobacter eikastus rhodopsin 2 (KR2) is a light-driven Na(+) pump found in marine bacterium. KR2 pumps Li(+) and Na(+), but it becomes an H(+) pump in the presence of K(+), Rb(+), and Cs(+). Site-directed mutagenesis of the cytoplasmic surface successfully converted KR2 into a light-driven K(+) pump, suggesting that ion selectivity is determined at the cytoplasmic surface. Here we extended this research and successfully created a light-driven Cs(+) pump. KR2 N61L/G263F pumps Cs(+) as well as other monovalent cations in the presence of a protonophore. Ion-transport activities correlated with the additive volume of the residues at 61 and 263. The result suggests that an ion-selectivity filter is affected by these two residues and functions by strict exclusion of K(+) and larger cations in the wild type (N61/G263). In contrast, introduction of large residues possibly destroys local structures of the ion-selectivity filter, leading to the permeation of K(+) (P61/W263) and Cs(+) (L61/F263).
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.
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: Yoshitaka
authors.initials: Y
authors.lastname: Kato
authors.affiliation: Department of Biological Sciences, Graduate School of Science, The University of Tokyo , 2-11-16 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan.
authors.forename: Hideaki E
authors.initials: HE
authors.lastname: Kato
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 (JST) , 4-1-8 Honcho Kawaguchi, Saitama, 332-0012, Japan.
authors.forename: Keiichi
authors.initials: K
authors.lastname: Inoue
authors.affiliation: Department of Biological Sciences, Graduate School of Science, The University of Tokyo , 2-11-16 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan.
authors.forename: Osamu
authors.initials: O
authors.lastname: Nureki
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.
authors.forename: Hideki
authors.initials: H
authors.lastname: Kandori
keywords: cesium; ion selectivity; ion-pumping rhodopsin; proteins; structure-based functional design