Crystal Structure and Biochemical Characterization of an Aminopeptidase LapB from Legionella pneumophila.

Aminopeptidases are a group of exopeptidases that catalyze the removal of a wide range of N-terminal amino acid residues from peptides and proteins. They have many important commercial applications in the food industry. We determined the crystal structure of an aminopeptidase LapB from Legionella pneumophila. The overall structure reveals that the N-terminal protease-associated (PA) domain presents a new fold and shields the active site cavity of the conserved C-terminal peptidase domain. The steady-state kinetic analysis of LapB and the PA domain deletion mutant indicate that the PA domain inhibited enzyme activity of the peptidase domain. Interestingly, the activity of LapB was largely increased by various organic solvents such as ethanol, propanol, and methanol at the concentration of 60% (v/v). CD analysis provided evidence that organic solvents induce the PA domain conformational changes that eliminate the inhibition role. The unique properties indicate the application potential of LapB in the food processing industry.