Enzyme Laboratory, National Food Research Institute^* Department of Structural Biology, Graduate School of Pharmaceutical Sciences, Hokkaido University^**
○Satoru Nirasawa^* Masataka Horiuch^** Nobuo N Suzuki^** Kiyohiro Takahashi^** Fuyuhiko Inagaki^** Kiyoshi Hayashi^*

Aminopeptidases from Aeromonas caviae (apAC) and Vibrio proteolyticus (apVP) are translated as a prepro-enzyme consisting of several domains; a signal peptide, an N-terminal propeptide, a mature region and a C-terminal propeptide. The N-terminal propeptide acts as an intramolecular chaperone to assist the folding of enzymes and shows inhibitory activity toward their cognate mature enzymes. These aminopeptidases belong into clan MH. The peptidases in clan MH are cocatalytic zinc peptidases containing two atoms of zinc per molecule. Clan MH contains aminopeptidases, carboxypeptidases, dipeptidases and tripeptidases. The tertiary structures have been determined for aminopeptidase S, glutamate carboxypeptidase II and apVP, and each shows a six-stranded beta-sheet surrounded by helices. apVP is the type structure for clan MH. There are several members of the clan that are not known to be peptidases, for example the transferrin receptor and aminoacylase. Up to now, the structure of pro-enzyme consisting the N-terminal propeptide in the clan MH is unknown. In the present study, we determined a structure of pro-form of a chimeric aminopeptidase by replacing the N-terminal propeptide of apVP with that of apAC.