Characterization and phylogenetic analysis of a thermostable N-carbamoyl-L-amino acid amidohydrolase from Bacillus kaustophilus CCRC11223

A thermostable N-carbamoyl-L-amino acid amidohydrolase (L-N-carbamoylase) gene composed of an 1,230-bp ORF encoding a 44.3-kDa protein was cloned from the thermophile Bacillus kaustophilus CCRC11223. This L-N-carbamoylase contained six cysteine residues that form three disulfide bridges. The purified L-N-carbamoylase was stringently L-specific and exhibited high activity in the hydrolysis of N-carbamoyl-L-homophenylalanine. N-carbamoyl derivatives of beta-alanine, beta-amino-isobutyric acids, L-tryptophan, and D-specific amino acids were not recognized as substrates. The L-N-carbamoylase required the divalent metal ions Mn2+, Co2+, and Ni2+ for increasing activity. The pH and temperature optima of the enzyme were pH 7.4 and 70 degreesC, respectively. This enzyme was completely thermostable at 50degreesC for 36 days in the presence of D- and/or L-specific substrates. Phylogenetic analysis of the available amino acid sequences of N-carbamoyl and N-acyl amino acid amidohydrolases from the three main kingdoms of life showed that they can be divided, into four distinct families. The B. kaustophilus enzyme could be classified into the family Of L-N-carbamoylases and some beta-ureidopropionases, but did not hydrolyze beta-ureidopropionates.