title: Crystal structures of rat anionic trypsin complexed with the protein inhibitors APPI and BPTI.
abstract: The crystal structure of rat anionic trypsin D189G/G226D has been determined in complexes with each of the protein inhibitors APPI (amyloid beta-protein precursor inhibitor domain) and BPTI (bovine pancreatic trypsin inhibitor) at resolutions of 2.5 A and 2.1 A, respectively. Comparisons with the structure of the bovine trypsin-BPTI complex show that the enzyme-inhibitor interactions in rat trypsin are dominated to a much greater degree by attractive and repulsive electrostatic forces. Decreased structural complementarity in the flanking regions of the interface formed with BPTI is reflected in significantly weaker inhibition relative to bovine trypsin. The primary active site loop of BPTI adopts slightly different conformations when bound to rat and cow trypsins, reflecting a broader entrance to the binding pocket in the former. Tight complementarity of each loop conformer to the respective active sites then gives rise to significantly different overall orientations of the inhibitor when bound to the two enzymes. The crystal structures of trypsin bound to these protein inhibitors are excellent models of the Michaelis complexes, which permit visualization of substrate interactions both N and C-terminal to the cleaved bond, while maintaining identical reaction chemistry. They will be uniquely useful to the structure-function analysis of variant rat trypsin enzymes.
authors.affiliation: Department of Pharmaceutical Chemistry, University of California, San Francisco 94143-0446.
authors.forename: J J
authors.initials: JJ
authors.lastname: Perona
authors.forename: C A
authors.initials: CA
authors.lastname: Tsu
authors.forename: C S
authors.initials: CS
authors.lastname: Craik
authors.forename: R J
authors.initials: RJ
authors.lastname: Fletterick
mesh_terms: D000595:Amino Acid Sequence; D016564:Amyloid beta-Protein Precursor / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000494:pharmacology; D000818:Animals; D007611:Aprotinin / Q000737:chemistry* / Q000494:pharmacology; D001665:Binding Sites; D002384:Catalysis; D002417:Cattle; D003545:Cysteine / Q000737:chemistry; D004220:Disulfides / Q000737:chemistry; D006860:Hydrogen Bonding; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D051381:Rats; D014357:Trypsin / Q000737:chemistry* / Q000378:metabolism; D014961:X-Ray Diffraction
chemical_list: D016564:Amyloid beta-Protein Precursor; D004220:Disulfides; D007611:Aprotinin; D014357:Trypsin; D003545:Cysteine