title: Characterization of a Cyanobacterial Chloride-pumping Rhodopsin and Its Conversion into a Proton Pump.
abstract: Light-driven ion-pumping rhodopsins are widely distributed in microorganisms and are now classified into the categories of outward H(+) and Na(+) pumps and an inward Cl(-) pump. These different types share a common protein architecture and utilize the photoisomerization of the same chromophore, retinal, to evoke photoreactions. Despite these similarities, successful pump-to-pump conversion had been confined to only the H(+) pump bacteriorhodopsin, which was converted to a Cl(-) pump in 1995 by a single amino acid replacement. In this study we report the first success of the reverse conversion from a Cl(-) pump to a H(+) pump. A novel microbial rhodopsin (MrHR) from the cyanobacterium Mastigocladopsis repens functions as a Cl(-) pump and belongs to a cluster that is far distant from the known Cl(-) pumps. With a single amino acid replacement, MrHR is converted to a H(+) pump in which dissociable residues function almost completely in the H(+) relay reactions. MrHR most likely evolved from a H(+) pump, but it has not yet been highly optimized into a mature Cl(-) pump.
authors.affiliation: From the Faculty of Advanced Life Science, Hokkaido University, Sapporo 060-0810, Japan.
authors.forename: Takatoshi
authors.initials: T
authors.lastname: Hasemi
authors.affiliation: From the Faculty of Advanced Life Science, Hokkaido University, Sapporo 060-0810, Japan kikukawa@sci.hokudai.ac.jp.
authors.forename: Takashi
authors.initials: T
authors.lastname: Kikukawa
authors.affiliation: From the Faculty of Advanced Life Science, Hokkaido University, Sapporo 060-0810, Japan.
authors.forename: Naoki
authors.initials: N
authors.lastname: Kamo
authors.affiliation: From the Faculty of Advanced Life Science, Hokkaido University, Sapporo 060-0810, Japan.
authors.forename: Makoto
authors.initials: M
authors.lastname: Demura
mesh_terms: D000222:Adaptation, Physiological / Q000528:radiation effects; D001436:Bacteriorhodopsins / Q000737:chemistry / Q000378:metabolism*; D002712:Chlorides / Q000378:metabolism*; D000458:Cyanobacteria / Q000378:metabolism* / Q000528:radiation effects; D004926:Escherichia coli / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007536:Isomerism; D007700:Kinetics; D008027:Light; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D010802:Phylogeny; D017494:Proton Pumps / Q000378:metabolism*; D012172:Retinaldehyde / Q000737:chemistry / Q000378:metabolism; D013057:Spectrum Analysis
chemical_list: D002712:Chlorides; D050505:Mutant Proteins; D017494:Proton Pumps; D001436:Bacteriorhodopsins; D012172:Retinaldehyde
keywords: bioenergetics; membrane protein; microbial rhodopsin; photobiology; photoreceptor; proton pump; retinal proteins