A noncanonical mechanism of carboxypeptidase inhibition revealed by the crystal structure of the Tri-Kunitz SmCI in complex with human CPA4

Structure. 2013 Jul 2;21(7):1118-26. doi: 10.1016/j.str.2013.04.021. Epub 2013 Jun 6.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Amino Acid Substitution
  • Animals
  • Carboxypeptidases A / chemistry*
  • Catalytic Domain
  • Crystallography, X-Ray
  • Humans
  • Hydrogen Bonding
  • Models, Molecular
  • Molecular Sequence Data
  • Peptide Fragments / chemistry
  • Peptide Fragments / genetics
  • Polychaeta / chemistry
  • Protease Inhibitors / chemistry*
  • Protein Binding
  • Protein Interaction Domains and Motifs
  • Protein Structure, Secondary

Substances

  • Peptide Fragments
  • Protease Inhibitors
  • CPA4, human
  • Carboxypeptidases A

Associated data

  • PDB/4BD9