Comparative biochemistry of bacterial N-acyl-D-amino acid amidohydrolase

N-acyl-D-amino acid amidohydrolases can be classified into three types base d on substrate specificity. D-aminoacylase has been reported to occur in a very few bacteria such as Pseudomonas. Streptomyces. and Alcaligenes. N-acy l-D-aspartate ami dohydrolase (D-AAase) has been reported in only Alcaligen es xylosoxydans subsp. xylosoxydans A-6 (Alcaligenes A-6) while N-acyl-D-gl utamate amidohydrolase (D-AGase) has been isolated in two stains of Pseudom onas sp. 5f-1 and Alcaligenes A-6. The physiological roles of these enzymes in these microbes are not clear. They are individually characteristic in t heir substrate specificities. inducer profiles, inhibitors, isoelectric poi nts. metal dependency, and some physicochemical properties. The primary str uctures of all the three types of N-acyl-D-amino acid amidohydrolases from Alcaligenes A-6 were determined from their nucleotide sequences. Comparison of their primary structures revealed high homology (46-56%) between the di fferent enzymes. The three enzymes showed 26-27% sequence homology with L-a minoacylases from Bacillus stearothermophilus, porcine, and human. Chemical modification and site-directed mutagenesis identified the histidyl residue s essential for catalysis. The Alcaligenes N-acyl-D-amino acid amidohydrola ses share significant sequence similarities with some members of the urease -related amidohydrolase superfamily proposed by Helm and Sander [L. Helm, C . Sander. Proteins: Structure, Function and Genetics 28 (1997) 72]. (C) 200 1 Elsevier Science B.V. All rights reserved.