title: Crystal structure of Escherichia coli-expressed Haloarcula marismortui bacteriorhodopsin I in the trimeric form.
abstract: Bacteriorhodopsins are a large family of seven-helical transmembrane proteins that function as light-driven proton pumps. Here, we present the crystal structure of a new member of the family, Haloarcula marismortui bacteriorhodopsin I (HmBRI) D94N mutant, at the resolution of 2.5 Å. While the HmBRI retinal-binding pocket and proton donor site are similar to those of other archaeal proton pumps, its proton release region is extended and contains additional water molecules. The protein's fold is reinforced by three novel inter-helical hydrogen bonds, two of which result from double substitutions relative to Halobacterium salinarum bacteriorhodopsin and other similar proteins. Despite the expression in Escherichia coli and consequent absence of native lipids, the protein assembles as a trimer in crystals. The unique extended loop between the helices D and E of HmBRI makes contacts with the adjacent protomer and appears to stabilize the interface. Many lipidic hydrophobic tail groups are discernible in the membrane region, and their positions are similar to those of archaeal isoprenoid lipids in the crystals of other proton pumps, isolated from native or native-like sources. All these features might explain the HmBRI properties and establish the protein as a novel model for the microbial rhodopsin proton pumping studies.
authors.affiliation: Institute of Complex Systems (ICS-6) Structural Biochemistry, Research Centre Jülich GmbH, Jülich, Germany; Laboratory for advanced studies of membrane proteins, Moscow institute of physics and technology, Dolgoprudniy, Russia.
authors.forename: Vitaly
authors.initials: V
authors.lastname: Shevchenko
authors.affiliation: Laboratory for advanced studies of membrane proteins, Moscow institute of physics and technology, Dolgoprudniy, Russia; Univ. Grenoble Alpes, IBS, Grenoble, France; CNRS, IBS, Grenoble, France; CEA, IBS, Grenoble, France.
authors.forename: Ivan
authors.initials: I
authors.lastname: Gushchin
authors.affiliation: Laboratory for advanced studies of membrane proteins, Moscow institute of physics and technology, Dolgoprudniy, Russia; Univ. Grenoble Alpes, IBS, Grenoble, France; CNRS, IBS, Grenoble, France; CEA, IBS, Grenoble, France.
authors.forename: Vitaly
authors.initials: V
authors.lastname: Polovinkin
authors.affiliation: Institute of Complex Systems (ICS-6) Structural Biochemistry, Research Centre Jülich GmbH, Jülich, Germany.
authors.forename: Ekaterina
authors.initials: E
authors.lastname: Round
authors.affiliation: Institute of Complex Systems (ICS-6) Structural Biochemistry, Research Centre Jülich GmbH, Jülich, Germany; Laboratory for advanced studies of membrane proteins, Moscow institute of physics and technology, Dolgoprudniy, Russia.
authors.forename: Valentin
authors.initials: V
authors.lastname: Borshchevskiy
authors.affiliation: Laboratory for advanced studies of membrane proteins, Moscow institute of physics and technology, Dolgoprudniy, Russia; Univ. Grenoble Alpes, IBS, Grenoble, France; CNRS, IBS, Grenoble, France.
authors.forename: Petr
authors.initials: P
authors.lastname: Utrobin
authors.affiliation: European Synchrotron Radiation Facility, Grenoble, France.
authors.forename: Alexander
authors.initials: A
authors.lastname: Popov
authors.affiliation: Institute of Complex Systems (ICS-6) Structural Biochemistry, Research Centre Jülich GmbH, Jülich, Germany.
authors.forename: Taras
authors.initials: T
authors.lastname: Balandin
authors.affiliation: Laboratory for advanced studies of membrane proteins, Moscow institute of physics and technology, Dolgoprudniy, Russia.
authors.forename: Georg
authors.initials: G
authors.lastname: Büldt
authors.affiliation: Institute of Complex Systems (ICS-6) Structural Biochemistry, Research Centre Jülich GmbH, Jülich, Germany; Laboratory for advanced studies of membrane proteins, Moscow institute of physics and technology, Dolgoprudniy, Russia; Univ. Grenoble Alpes, IBS, Grenoble, France; CNRS, IBS, Grenoble, France; CEA, IBS, Grenoble, France; European Synchrotron Radiation Facility, Grenoble, France.
authors.forename: Valentin
authors.initials: V
authors.lastname: Gordeliy
mesh_terms: D001436:Bacteriorhodopsins / Q000737:chemistry* / Q000235:genetics; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000235:genetics; D019614:Haloarcula marismortui / Q000737:chemistry*; D006860:Hydrogen Bonding; D057927:Hydrophobic and Hydrophilic Interactions; D055503:Protein Multimerization; D017433:Protein Structure, Secondary; D014867:Water / Q000737:chemistry
chemical_list: D014867:Water; D001436:Bacteriorhodopsins