title: Structural insights into the proton pumping by unusual proteorhodopsin from nonmarine bacteria.
abstract: Light-driven proton pumps are present in many organisms. Here, we present a high-resolution structure of a proteorhodopsin from a permafrost bacterium, Exiguobacterium sibiricum rhodopsin (ESR). Contrary to the proton pumps of known structure, ESR possesses three unique features. First, ESR's proton donor is a lysine side chain that is situated very close to the bulk solvent. Second, the α-helical structure in the middle of the helix F is replaced by 3(10)- and π-helix-like elements that are stabilized by the Trp-154 and Asn-224 side chains. This feature is characteristic for the proteorhodopsin family of proteins. Third, the proton release region is connected to the bulk solvent by a chain of water molecules already in the ground state. Despite these peculiarities, the positions of water molecule and amino acid side chains in the immediate Schiff base vicinity are very well conserved. These features make ESR a very unusual proton pump. The presented structure sheds light on the large family of proteorhodopsins, for which structural information was not available previously.
authors.affiliation: Institut de Biologie Structurale J.-P. Ebel, Université Grenoble Alpes, 38027 Grenoble, France.
authors.forename: Ivan
authors.initials: I
authors.lastname: Gushchin
authors.forename: Pavel
authors.initials: P
authors.lastname: Chervakov
authors.forename: Pavel
authors.initials: P
authors.lastname: Kuzmichev
authors.forename: Alexander N
authors.initials: AN
authors.lastname: Popov
authors.forename: Ekaterina
authors.initials: E
authors.lastname: Round
authors.forename: Valentin
authors.initials: V
authors.lastname: Borshchevskiy
authors.forename: Andrii
authors.initials: A
authors.lastname: Ishchenko
authors.forename: Lada
authors.initials: L
authors.lastname: Petrovskaya
authors.forename: Vladimir
authors.initials: V
authors.lastname: Chupin
authors.forename: Dmitry A
authors.initials: DA
authors.lastname: Dolgikh
authors.forename: Alexander S
authors.initials: AS
authors.lastname: Arseniev
authors.forename: Alexander A
authors.initials: AA
authors.lastname: Arseniev
authors.forename: Mikhail
authors.initials: M
authors.lastname: Kirpichnikov
authors.forename: Valentin
authors.initials: V
authors.lastname: Gordeliy
mesh_terms: D001406:Bacillaceae / Q000737:chemistry*; D001426:Bacterial Proteins / Q000737:chemistry*; D018360:Crystallography, X-Ray; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012243:Rhodopsin / Q000737:chemistry*; D025604:Rhodopsins, Microbial; D013329:Structure-Activity Relationship
chemical_list: D001426:Bacterial Proteins; D025604:Rhodopsins, Microbial; C413548:proteorhodopsin; D012243:Rhodopsin
keywords: bacteriorhodopsin; photocycle; retinal; retinylidene protein