A light-driven sodium ion pump in marine bacteria

• Published in: Nature communications 2013-04, Vol.4 (1), p.1678
• Main Authors: Inoue, Keiichi, Ono, Hikaru, Abe-Yoshizumi, Rei, Yoshizawa, Susumu, Ito, Hiroyasu, Kogure, Kazuhiro, Kandori, Hideki
• Format: Article
• Language: English
• Subjects: 631/326/41/1969; 631/45/49/1142; 631/57/2272; Bacteria; Chloride; E coli; Energy; Flavobacterium - metabolism; Humanities and Social Sciences; Light; Lithium; Marine Biology; Microorganisms; Models, Molecular; multidisciplinary; Mutation; Potassium; Protons; Science; Science (multidisciplinary); Sodium; Sodium-Potassium-Exchanging ATPase - chemistry; Sodium-Potassium-Exchanging ATPase - genetics; Sodium-Potassium-Exchanging ATPase - metabolism; Water Microbiology
• ISSN: 2041-1723
• DOI: 10.1038/ncomms2689

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. Light-driven proton-pumping rhodopsins are widely distributed in microorganisms and convert sunlight energy into proton gradients. Inoue et al . report the discovery of a light-driven sodium ion pump from marine bacteria.