Cloning and sequencing of a novel meta-cleavage dioxygenase gene whose product is involved in degradation of gamma-hexachlorocyclohexane in Sphingomonas paucimobilis

Sphingomonas (formerly Pseudomonas) paucimobilis UT26 utilizes gamma-hexach lorocyclohexane (gamma-HCH), a halogenated organic insecticide, as a sole s ource of carbon and energy. In a previous study, we showed that gamma-HCH i s degraded to chlorohydroquinone (CHQ) and then to hydroquinone (HQ), altho ugh the rate of reaction from CHQ to HQ was slow (K. Miyauchi, S. K. Suh, Y . Nagata, and M. Takagi, J. Bacteriol. 180: 1354-1359, 1998). In this study , we cloned and characterized a gene, designated linE, which is located ups tream of linD and is directly involved in the degradation of CHQ. The LinE protein consists of 321 amino acids, and all of the amino acids which are r eported to be essential for the activity of meta-cleavage dioxygenases are conserved in LinE. Escherichia coli overproducing LinE could convert both C HQ and HQ, producing gamma-hydroxymuconic semialdehyde and maleylacetate, r espectively, with consumption of O-2 but could not convert catechol, which is one of the major substrates for meta-cleavage dioxygenases. LinE seems t o be resistant to the acylchloride, which is the ring cleavage product of C HQ and which seems to react with water to be converted to maleylacetate. Th ese results indicated that LinE is a novel type of meta-cleavage dioxygenas e, designated (chloro)hydroquinone 1,2-dioxygenase, which cleaves aromatic rings with two hydroxyl groups at para positions preferably. This study rep resents a direct demonstration of a new type of ring cleavage pathway for a romatic compounds, the hydroquinone pathway.