title: A noncanonical mechanism of carboxypeptidase inhibition revealed by the crystal structure of the Tri-Kunitz SmCI in complex with human CPA4.
abstract: The crystal structure of SmCI (Sabellastarte magnifica carboxypeptidase inhibitor) has been determined in complex with human carboxypeptidase A4 (hCPA4). SmCI is composed by three BPTI/Kunitz domains, each one displaying high structural homology and functionality with serine protease inhibitors. Moreover, SmCI possesses a distinctive capability to inhibit metallo-carboxypeptidases, constituting a bifunctional metallocarboxy- and serine protease inhibitor. The structure of the 1:1 complex of SmCI with hCPA4 reveals a noncanonical mechanism of carboxypeptidase inhibition, which surprisingly occurs mainly via the N-terminal segment, which penetrates into the active site groove of the enzyme. Mutagenesis and biochemical analysis confirm the major role of the N-terminal segment in the inhibition of carboxypeptidases. SmCI represents a tri-Kunitz serine protease inhibitor adapted to inhibit metallo-carboxypeptidases and discloses an unusual mechanism of inhibition by the N-terminal segment, emulating the "classical" C-terminal substrate-like inhibition.
authors.affiliation: Centro de Estudio de Proteínas, Facultad de Biología, Universidad de la Habana, Cuba 10400.
authors.forename: Maday
authors.initials: M
authors.lastname: Alonso del Rivero
authors.forename: Mey L
authors.initials: ML
authors.lastname: Reytor
authors.forename: Sebastian A
authors.initials: SA
authors.lastname: Trejo
authors.forename: María A
authors.initials: MA
authors.lastname: Chávez
authors.forename: Francesc X
authors.initials: FX
authors.lastname: Avilés
authors.forename: David
authors.initials: D
authors.lastname: Reverter
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D043422:Carboxypeptidases A / Q000737:chemistry*; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D006801:Humans; D006860:Hydrogen Bonding; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry / Q000235:genetics; D011077:Polychaeta / Q000737:chemistry; D011480:Protease Inhibitors / Q000737:chemistry*; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D017433:Protein Structure, Secondary
chemical_list: D010446:Peptide Fragments; D011480:Protease Inhibitors; C539656:CPA4, human; D043422:Carboxypeptidases A