title: A light-driven sodium ion pump in marine bacteria.
abstract: Light-driven proton-pumping rhodopsins are widely distributed in many microorganisms. They convert sunlight energy into proton gradients that serve as energy source of the cell. Here we report a new functional class of a microbial rhodopsin, a light-driven sodium ion pump. We discover that the marine flavobacterium Krokinobacter eikastus possesses two rhodopsins, the first, KR1, being a prototypical proton pump, while the second, KR2, pumps sodium ions outward. Rhodopsin KR2 can also pump lithium ions, but converts to a proton pump when presented with potassium chloride or salts of larger cations. These data indicate that KR2 is a compatible sodium ion-proton pump, and spectroscopic analysis showed it binds sodium ions in its extracellular domain. These findings suggest that light-driven sodium pumps may be as important in situ as their proton-pumping counterparts.
authors.affiliation: Department of Frontier Materials, Nagoya Institute of Technology, Showa-ku, Nagoya 466-8555, Japan.
authors.forename: Keiichi
authors.initials: K
authors.lastname: Inoue
authors.forename: Hikaru
authors.initials: H
authors.lastname: Ono
authors.forename: Rei
authors.initials: R
authors.lastname: Abe-Yoshizumi
authors.forename: Susumu
authors.initials: S
authors.lastname: Yoshizawa
authors.forename: Hiroyasu
authors.initials: H
authors.lastname: Ito
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Kogure
authors.forename: Hideki
authors.initials: H
authors.lastname: Kandori
mesh_terms: D005417:Flavobacterium / Q000378:metabolism*; D008386:Marine Biology; D008958:Models, Molecular; D009154:Mutation; D000254:Sodium-Potassium-Exchanging ATPase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014871:Water Microbiology
chemical_list: D000254:Sodium-Potassium-Exchanging ATPase