Biocatalytic Potential of a Mycobacterial Aminoacylase for Synthesis of N-Acyl-L-Amino Acids in Aqueous Media.

In this study, we present an investigation of the recently identified aminoacylase MsAA for the synthesis of N-acyl-L-amino acids, focusing on N-lauroyl-L-methionine. We found optimal reaction conditions at pH 8.0 and a temperature of 40-45°C with substrate concentrations of 400 mM methionine and 150 mM lauric acid. The highest product concentration of 100 mM was achieved with 67% substrate conversion after 72 h reaction at 40°C and pH 8.0. The reaction could be upscaled with a nearly identical reaction course. Several other fatty acids were also found to be substrates of this enzyme. Besides methionine, only hydrophobic amino acids were accepted for acylation. For a detailed analysis of the catalytic reaction mechanism of MsAA, we performed in silico protein modeling studies. Molecular docking of lauric acid and methionine to the predicted MsAA structure resulted in a similar mode of substrate binding as described for the related N-succinyl-L,L-diaminopimelic acid desuccinylase from Haemophilus influenzae. Differences in amino acid sequence of structurally conserved substrate-binding residues explain the distinct substrate scope of the enzymes. The structure-function relationship of relevant amino acid residues was validated by a mutagenesis study.