title: The light-driven sodium ion pump: A new player in rhodopsin research.
abstract: Rhodopsins are one of the most studied photoreceptor protein families, and ion-translocating rhodopsins, both pumps and channels, have recently attracted broad attention because of the development of optogenetics. Recently, a new functional class of ion-pumping rhodopsins, an outward Na+pump, was discovered, and following structural and functional studies enable us to compare three functionally different ion-pumping rhodopsins: outward proton pump, inward Cl-pump, and outward Na+pump. Here, we review the current knowledge on structure-function relationships in these three light-driven pumps, mainly focusing on Na+pumps. A structural and functional comparison reveals both unique and conserved features of these ion pumps, and enhances our understanding about how the structurally similar microbial rhodopsins acquired such diverse functions. We also discuss some unresolved questions and future perspectives in research of ion-pumping rhodopsins, including optogenetics application and engineering of novel rhodopsins.
authors.affiliation: Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA, USA.
authors.forename: Hideaki E
authors.initials: HE
authors.lastname: Kato
authors.affiliation: Department of Frontier Materials, Nagoya Institute of Technology, Nagoya, Japan.|OptoBioTechnology Research Center, Nagoya Institute of Technology, Nagoya, Japan.|PRESTO, Japan Science and Technology Agency, Kawaguchi, Saitama, Japan.
authors.forename: Keiichi
authors.initials: K
authors.lastname: Inoue
authors.affiliation: Department of Frontier Materials, Nagoya Institute of Technology, Nagoya, Japan.|OptoBioTechnology Research Center, Nagoya Institute of Technology, Nagoya, Japan.
authors.forename: Hideki
authors.initials: H
authors.lastname: Kandori
authors.affiliation: Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Bunkyo-ku, Tokyo, Japan.
authors.forename: Osamu
authors.initials: O
authors.lastname: Nureki
mesh_terms: D000818:Animals; D027682:Cation Transport Proteins / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D008027:Light; D008958:Models, Molecular; D062308:Optogenetics; D011487:Protein Conformation; D012243:Rhodopsin / Q000737:chemistry / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*
chemical_list: D027682:Cation Transport Proteins; D012243:Rhodopsin; D012964:Sodium
keywords: KR2; crystal structure; light-driven ion pump; optogenetics; retinal; rhodopsin; structural biology