Analysis of three 2,3-dihydroxybiphenyl 1,2-dioxygenases found in Rhodococcus globerulus P6. Identification of a new family of extradiol dioxygenases

Abstract

The polychlorobiphenyl-degrading bacterium Rhodococcus globerulus P6 contains three bphC genes encoding 2,3-dihydroxybiphenyl 1,2-dioxygenases. One of them, bphC1, is clustered with the bphB gene which encodes 2,3-dihydroxy-4-phenylhexa-4,6-diene dehydrogenase and constitutes part of the bph operon specifying the degradation of biphenyl. The nucleotide sequence of bphB and the three bphC genes has been determined. The protein products of the bphBC1 gene cluster were found to exhibit significant homology with the corresponding proteins of analogous degradative pathways in Gram-negative bacteria; the highest homology was in those of the toluene degradation pathway of Pseudomonas putida strain F1. No homology was found between bphC2 and bphC3 and any other sequence in the database. At least two of the three meta cleavage enzymes are inducible by biphenyl. 2,3-Dihydroxybiphenyl 1,2-dioxygenase II, encoded by the bphC2 gene, was purified to apparent homogeneity from a recombinant Escherichia coli strain. The enzyme differed from other extradiol dioxygenases in having a subunit molecular mass of 21 kDa and a hexameric structure. The enzyme contains one tightly bound iron per subunit. These characteristics demonstrate that the 2,3-dihydroxybiphenyl 1,2-dioxygenases encoded by bphC2 and bphC3 belong to a new class of extradiol dioxygenases.