Characterization of full length and truncated type I human methionine aminopeptidases expressed from Escherichia coli.

Methionine aminopeptidase (MetAP) carries out an essential posttranslational modification of nascent proteins by removing the initiator methionine and is recognized as a potential target for developing antibacterial, antifungal, and anticancer agents. We have established an Escherichia coli expression system for human type I MetAP (HsMetAP1) and characterized the full length HsMetAP1 and its N-terminal-truncated mutants HsMetAP1(Delta1-66) and HsMetAP1(Delta1-135) for hydrolysis of several thiopeptolide and peptide substrates and inhibition by a series of nonpeptidic inhibitors. Although the N-terminal extension with zinc finger motifs in HsMetAP1 is not required for enzyme activity, it has a significant impact on the interaction of the enzyme with substrates and inhibitors. In hydrolysis of the thiopeptolide substrates, a relaxation of stringent specificity for the terminal methionine was observed in the truncated mutants. However, this relaxation of specificity was not detectable in hydrolysis of tripeptide or tetrapeptide substrates. Several nonpeptidic inhibitors showed potent inhibition of the mutant HsMetAP1(Delta1-66) but exhibited only weak or no inhibition of the full length enzyme. With the recombinant HsMetAP1 available, we have identified several MetAP inhibitors with submicromolar inhibitory potencies against E. coli MetAP (EcMetAP1) that do not affect HsMetAP1. These results have demonstrated the possibility of developing MetAP inhibitors as antibacterial agents with minimum human toxicity. In addition, micromolar inhibitors of HsMetAP1 identified in this study can serve as tools for investigating the functions of HsMetAP1 in physiological and pathological processes.