title: Recognition between a bacterial ribonuclease, barnase, and its natural inhibitor, barstar.
abstract: BACKGROUND
  Protein-protein recognition is fundamental to most biological processes. The information we have so far on the interfaces between proteins comes largely from several protease-inhibitor and antigen-antibody complexes. Barnase, a bacterial ribonuclease, and barstar, its natural inhibitor, form a tight complex which provides a good model for the study and design of protein-protein non-covalent interactions.
  
  
  RESULTS
  Here we report the structure of a complex between barnase and a fully functional mutant of barstar determined by X-ray analysis. Barstar is composed of three parallel alpha-helices stacked against a three-stranded parallel, beta-sheet, and sterically blocks the active site of the enzyme with an alpha-helix and adjacent loop. The buried surface in the interface between the two molecules totals 1630 A2. The barnase-barstar complex is predominantly stabilized by charge interactions involving positive charges in the active site of the enzyme. Asp39 of barstar binds to the phosphate-binding site of barnase, mimicking enzyme-substrate interactions.
  
  
  CONCLUSIONS
  The phosphate-binding site of the enzyme is the anchor point for inhibitor binding. We propose that this is also likely to be the case for other ribonuclease inhibitors.
authors.affiliation: Laboratoire de Physique, CNRS, UPR 180, Centre d'Etudes Pharmaceutiques, 92296 Châtenay-Malabry Cedex, France.
authors.forename: V
authors.initials: V
authors.lastname: Guillet
authors.forename: A
authors.initials: A
authors.lastname: Lapthorn
authors.forename: R W
authors.initials: RW
authors.lastname: Hartley
authors.forename: Y
authors.initials: Y
authors.lastname: Mauguen
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D018360:Crystallography, X-Ray; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D009154:Mutation; D010710:Phosphates / Q000378:metabolism; D011487:Protein Conformation; D012260:Ribonucleases / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D004791:Enzyme Inhibitors; D010710:Phosphates; C057438:barstar protein, Bacillus amyloliquefaciens; D012260:Ribonucleases; C019760:Bacillus amyloliquefaciens ribonuclease