A metal-dependent switch moderates activity of the hexameric M17 aminopeptidases.

The metal-dependent M17 aminopeptidases are conserved throughout all kingdoms of life. The large enzyme family is characterised by a conserved binuclear metal center and a distinctive homohexameric arrangement. To understand the mechanistic role of the hexameric assembly, we undertook an investigation of the structure and dynamics of the M17 aminopeptidase from P. falciparum, PfA-M17. We describe a novel structure of PfA-M17, which shows that the active sites of each trimer are linked by a dynamic loop, and that the loop movement is coupled with a drastic rearrangement of the binuclear metal center and substrate-binding pocket. Molecular dynamics simulations, supported by biochemical analyses of PfA-M17 variants, demonstrate that this rearrangement is inherent to PfA-M17, and that the transition between the active and inactive states is part of a dynamic regulatory mechanism. Key to the mechanism is a re-modelling of the binuclear metal center, which occurs in response to a signal from the neighbouring active site, and serves to moderate the rate of proteolysis under different environmental conditions. Therefore, this work has identified the precise mechanism by which oligomerization contributes to PfA-M17 function. Further, it has described a novel role for metal cofactors in the regulation of enzymes with implications for the wide range of metalloenzymes that operate via a two-metal ion catalytic center including DNA processing enzymes and metalloproteases.