Characterization of the Gene Encoding Catechol 2,3-Dioxygenase fromAchromobacter xylosoxidansKF701

Abstract

Catechol 2,3-dioxygenase (C23O) catalyzes ametacleavage of the aromatic ring in catechol to form 2-hydroxymuconic semialdehyde. A C23O gene was cloned from chromosomal DNA ofA. xylosoxidansKF701, a soil bacterium degrading biphenyl, and expressed inE. coliHB101. In substrate specificity to catechol and its analogs, the C23O exhibited the highest aromatic ring-fission activity to catechol, and its relative activity to other dihydroxylated aromatics was 4-chlorocatechol > 4-methylcatechol > 3-methylcatechol ⪢ 2,3-dihydroxybiphenyl. Aromatic ring-fission activity of the C23O to catechol was about 40-fold higher than that to 2,3-dihydroxybiphenyl. Nucleotide sequence analysis of the C23O gene fromA. xylosoxidansKF701 revealed an open reading frame consisting of 924 base pairs, and identified a putative ribosome-binding sequence (AGGTGA) at about 10 nucleotides upstream from the initiation codon. The open reading frame can encode a polypeptide chain with molecular weight of 34 kDa containing 307 amino acid residues. The deduced amino acid sequence of the C23O exhibited the highest homology with that of C23O fromPseudomonassp. IC with 96% identity, and the least homology with that of C23O fromP. putidaF1 with 22% identity among reported C23O sequences. Furthermore, comparison of the C23O sequence with other extradiol dioxygenases has led to identification of evolutionally conserved amino acid residues whose possible catalytic and structural roles are proposed.