A novel d-stereoselective amino acid amidase from Brevibacterium iodinum: Gene cloning, expression and characterization

The gene encoding d-stereoselective amino acid amide amidohydrolase (d-amino acid amidase, named DaaABi) was cloned from a chromosomal DNA library of Brevibacterium iodinum TPU 5850 and sequenced. The gene, daaABi, encoded a protein composed of 266 amino acids with a Mr of 30035. The deduced amino-acid sequence of the daaABi gene did not exhibit any similarity with any other previously reported d-amino acid amidases, but did show similarity with hypothetical class A β-lactamases. DaaABi protein was produced in Escherichia coli, purified to electrophoretic homogeneity, and characterized. The purified enzyme was about 290,000 based on gel filtration chromatography and about 30,000 based on SDS-polyacrylamide gel electrophoresis, suggesting that the enzyme is active as a decamer with identical subunits. DaaABi showed maximum activity at pH 7.2 and 35 °C. It exhibited strict d-stereoselective hydrolyzing activity towards a broad range of d-amino acid amides including d-methioninamide, d-lysinamide, d-glutaminamide, and d-phenylalaninamide, while l-amino acid amides, peptides composed of l- or d-amino acids, and β-lactam compounds could not serve as substrates for the enzyme. Almost complete hydrolysis of d-phenylalaninamide with highly strict d-stereoselectivity was achieved in 3 h from 180 mM of dl-phenylalaninamide using the purified DaaABi enzyme.