title: The crystal structures of the oligopeptide-binding protein OppA complexed with tripeptide and tetrapeptide ligands.
abstract: BACKGROUND
  The periplasmic oligopeptide-binding protein OppA has a remarkably broad substrate specificity, binding peptides of two or five amino-acid residues with high affinity, but little regard to sequence. It is therefore an ideal system for studying how different chemical groups can be accommodated in a protein interior. The ability of the protein to bind peptides of different lengths has been studied by co-crystallising it with different ligands.
  
  
  RESULTS
  Crystals of OppA from Salmonella typhimurium complexed with the peptides Lys-Lys-Lys (KKK) and Lys-Lys-Lys-Ala (KKKA) have been grown in the presence of uranyl ions which form important crystal contacts. These structures have been refined to 1.4 A and 2.1 A, respectively. The ligands are completely enclosed, their side chains pointing into large hydrated cavities and making few strong interactions with the protein.
  
  
  CONCLUSIONS
  Tight peptide binding by OppA arises from strong hydrogen bonding and electrostatic interactions between the protein and the main chain of the ligand. Different basic side chains on the protein form salt bridges with the C terminus of peptide ligands of different lengths.
authors: Department of Chemistry, University of York, UK.
authors: J R
authors: JR
authors: Tame
authors: E J
authors: EJ
authors: Dodson
authors: G
authors: G
authors: Murshudov
authors: C F
authors: CF
authors: Higgins
authors: A J
authors: AJ
authors: Wilkinson
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D002352:Carrier Proteins / Q000737:chemistry* / Q000378:metabolism; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D018360:Crystallography, X-Ray; D006680:HLA Antigens / Q000737:chemistry / Q000378:metabolism; D006860:Hydrogen Bonding; D008024:Ligands; D008074:Lipoproteins / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000378:metabolism*; D011107:Polylysine / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D012486:Salmonella typhimurium / Q000737:chemistry*; D014501:Uranium / Q000737:chemistry
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; D006680:HLA Antigens; D008024:Ligands; D008074:Lipoproteins; D009842:Oligopeptides; C499291:oligopeptide-binding protein, Salmonella typhimurium; C046506:oligopeptide-binding protein, bacteria; D011107:Polylysine; D014501:Uranium