title: The three-dimensional structures of tick carboxypeptidase inhibitor in complex with A/B carboxypeptidases reveal a novel double-headed binding mode.
abstract: The tick carboxypeptidase inhibitor (TCI) is a proteinaceous inhibitor of metallo-carboxypeptidases present in the blood-sucking tick Rhipicephalus bursa. The three-dimensional crystal structures of recombinant TCI bound to bovine carboxypeptidase A and to human carboxypeptidase B have been determined and refined at 1.7 A and at 2.0 A resolution, respectively. TCI consists of two domains that are structurally similar despite the low degree of sequence homology. The domains, each consisting of a short alpha-helix followed by a small twisted antiparallel beta-sheet, show a high level of structural homology to proteins of the beta-defensin-fold family. TCI anchors to the surface of mammalian carboxypeptidases in a double-headed manner not previously seen for carboxypeptidase inhibitors: the last three carboxy-terminal amino acid residues interact with the active site of the enzyme in a way that mimics substrate binding, and the N-terminal domain binds to an exosite distinct from the active-site groove. The structures of these complexes should prove valuable in the applications of TCI as a thrombolytic drug and as a basis for the design of novel bivalent carboxypeptidase inhibitors.
authors.affiliation: Institut de Biotecnologia i Biomedicina and Departament de Bioquímica i Biologia Molecular, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain.
authors.forename: Joan L
authors.initials: JL
authors.lastname: Arolas
authors.forename: Grzegorz M
authors.initials: GM
authors.lastname: Popowicz
authors.forename: Julia
authors.initials: J
authors.lastname: Lorenzo
authors.forename: Christian P
authors.initials: CP
authors.lastname: Sommerhoff
authors.forename: Robert
authors.initials: R
authors.lastname: Huber
authors.forename: Francesc X
authors.initials: FX
authors.lastname: Aviles
authors.forename: Tad A
authors.initials: TA
authors.lastname: Holak
mesh_terms: D020816:Amino Acid Motifs; D000818:Animals; D001665:Binding Sites; D043424:Carboxypeptidase B / Q000737:chemistry* / Q000378:metabolism; D002268:Carboxypeptidases / Q000037:antagonists & inhibitors*; D043422:Carboxypeptidases A / Q000737:chemistry* / Q000378:metabolism; D002417:Cattle; D018360:Crystallography, X-Ray; D030562:Databases, Protein; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D004926:Escherichia coli / Q000378:metabolism; D006801:Humans; D008958:Models, Molecular; D010179:Pancreas / Q000201:enzymology; D010843:Pichia / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D048494:Rhipicephalus; D013987:Ticks; D023083:beta-Defensins / Q000737:chemistry
chemical_list: D004791:Enzyme Inhibitors; D023083:beta-Defensins; D002268:Carboxypeptidases; D043422:Carboxypeptidases A; D043424:Carboxypeptidase B