Wc. Suen et al., DINITROTOLUENE DIOXYGENASE FROM BURKHOLDERIA SP STRAIN DNT - SIMILARITY TO NAPHTHALENE DIOXYGENASE, Journal of bacteriology, 178(16), 1996, pp. 4926-4934
2,4-Dinitrotoluene (DNT) dioxygenase from Burkholderia sp. strain DNT
catalyzes the initial oxidation of DNT to form 4-methyl-5-nitrocatecho
l (NNC) and nitrite. The displacement of the aromatic nitro group by d
ioxygenases has only recently been described, and nothing is known abo
ut the evolutionary origin of the enzyme systems that catalyze these r
eactions. We have shown previously that the gene encoding DNT dioxygen
ase is localized on a degradative plasmid within a 6,8-kb NsiI DNA fra
gment (W.-C. Suen and J. C. Spain, J. Bacteriol, 175:1831-1837, 1993).
We describe here the sequence analysts and the substrate range of the
enzyme system encoded by this fragment. Five open reading frames were
identified, four of which have a high degree of similarity (59 to 78%
identity) to the components of naphthalene dioxygenase (NDO) from Pse
udomonas strains. The conserved amino acid residues within NDO that ar
e involved in cofactor binding were also identified in the gene encodi
ng DNT dioxygenase. An Escherichia coli clone that expressed DNT dioxy
genase converted DNT to MNC and also converted naphthalene to (+)-cis-
(1R,2S)-dihydroxy-1,2-dihydronaphthalene. In contrast, the E. coli clo
ne that expressed NDO did not oxidize DNT. Furthermore, the enzyme sys
tems exhibit similar broad substrate specificities and can oxidize suc
h compounds as indole, indan, indene, phenetole, and acenaphthene. The
se results suggest that DNT dioxygenase and the NDO enzyme system shar
e a common ancestor.