title: Structure of the membrane channel porin from Rhodopseudomonas blastica at 2.0 A resolution.
abstract: The crystal structure of a membrane channel, homotrimeric porin from Rhodopseudomonas blastica has been determined at 2.0 A resolution by multiple isomorphous replacement and structural refinement. The current model has an R-factor of 16.5% and consists of 289 amino acids, 238 water molecules, and 3 detergent molecules per subunit. The partial protein sequence and subsequently the complete DNA sequence were determined. The general architecture is similar to those of the structurally known porins. As a particular feature there are 3 adjacent binding sites for n-alkyl chains at the molecular 3-fold axis. The side chain arrangement in the channel indicates a transverse electric field across each of the 3 pore eyelets, which may explain the discrimination against nonpolar solutes. Moreover, there are 2 significantly ordered girdles of aromatic residues at the nonpolar/polar borderlines of the interface between protein and membrane. Possibly, these residues shield the polypeptide conformation against adverse membrane fluctuations.
authors.affiliation: Institut für Organische Chemie und Biochemie, Albert-Ludwigs-Universität, Freiburg im Breisgau, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Kreusch
authors.forename: A
authors.initials: A
authors.lastname: Neubüser
authors.forename: E
authors.initials: E
authors.lastname: Schiltz
authors.forename: J
authors.initials: J
authors.lastname: Weckesser
authors.forename: G E
authors.initials: GE
authors.lastname: Schulz
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D003460:Crystallization; D018360:Crystallography, X-Ray; D050356:Lipid Metabolism; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D015394:Molecular Structure; D018272:Porins / Q000737:chemistry* / Q000378:metabolism; D017433:Protein Structure, Secondary; D012241:Rhodopseudomonas / Q000737:chemistry*
chemical_list: D046911:Macromolecular Substances; D018272:Porins