A Noncanonical Mechanism of Carboxypeptidase Inhibition Revealed by the Crystal Structure of the Tri-Kunitz SmCI in Complex with Human CPA4.

ALONSO DEL RIVERO M; REYTOR ML; TREJO SA; CHÁVEZ MA; AVILÉS FX; REVERTER D

STRUCTURE WITH FOLDING & DESIGN.

CELL PRESS

Lugar: United States; Año: 2013 p. 1118 - 1126

0969-2126

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.