Evidence That pcpA Encodes 2,6-Dichlorohydroquinone Dioxygenase, the Ring Cleavage Enzyme Required for Pentachlorophenol Degradation in Sphingomonas chlorophenolica Strain ATCC 39723

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Abstract
An enzyme that catalyzes an Fe2+-dependent reaction of 2, 6-dichlorohydroquinone with O2 has been isolated from Sphingomonas chlorophenolica sp. strain ATCC 39723, a soil microorganism capable of complete mineralization of pentachlorophenol. The product of the reaction is too unstable to allow spectroscopic characterization, but is apparently negatively charged and retains the two chlorine atoms of the substrate. The enzyme was partially sequenced using electrospray LC-MS, and one peptide was used to search the NCBInr database. This peptide matched a part of PcpA, a protein of unknown function that is induced in S. chlorophenolica in response to pentachlorophenol. Several other peptides could also be mapped onto the sequence of PcpA, suggesting that the enzyme is encoded by pcpA. PcpA has low but significant sequence similarity to an unusual class of extradiol dioxygenases. On the basis of the sequence analysis, the Fe2+ and O2 dependence of the enzyme, and the characteristics of the product, the enzyme is proposed to be a 2,6-dichlorohydroquinone dioxygenase. The position of ring cleavage has not yet been identified.