title: Porin conformation in the absence of calcium. Refined structure at 2.5 A resolution.
abstract: The crystal structure of porin from Rhodobacter capsulatus in the absence of divalent calcium ions has been refined to convergence at a resolution of 2.5 A using the simulated annealing refinement method. The final model consists of all 301 amino acid residues, 77 solvent molecules, one tris(hydroxymethyl)-aminomethane molecule and one unknown ligand modeled as n-octyltetraoxyethylene. A superposition with the previously described model containing three calcium ions showed structural changes at the segment 108-116 of the inner loop beta 5-beta 6, and at loops beta 8-beta 9 and beta 11-beta 12 at the extracellular side of the porin molecule. Evidence is presented that the conformational changes depend on the presence or absence of calcium ions. A possible influence on porin function is discussed.
authors.affiliation: Institut für Organische Chemie und Biochemie, Albert-Ludwigs-Universität, Freiburg im Breisgau, Germany.
authors.forename: M S
authors.initials: MS
authors.lastname: Weiss
authors.forename: G E
authors.initials: GE
authors.lastname: Schulz
mesh_terms: D000595:Amino Acid Sequence; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry*; D002118:Calcium / Q000737:chemistry*; D003198:Computer Simulation; D007473:Ion Channels; D008958:Models, Molecular; D008969:Molecular Sequence Data; D018272:Porins; D011487:Protein Conformation; D016354:Rhodobacter capsulatus; D014961:X-Ray Diffraction
chemical_list: D001425:Bacterial Outer Membrane Proteins; D007473:Ion Channels; D018272:Porins; D002118:Calcium