Bacterial Catabolism of a Lignin-derived β–5 Dimer

抄録

The β–5 linkage is an intermolecular linkage in lignin. Sphingobium sp. strain SYK-6 can assimilate various lignin-derived dimers, including a β–5 dimer, dehydrodiconiferyl alcohol. In SYK-6, the hydroxyl group at Cγ of the B-ring side chain of dehydrodiconiferyl alcohol is oxidized to generate the γ-carboxylic compound, DCA-C. Then, the hydroxyl group at Cγ of the A-ring side chain of DCA-C is oxidized to the carboxyl group to generate the dicarboxylic compound, DCA-CC. The carboxylic group at Cγ of the A-ring side chain of DCA-CC is decarboxylated, and the accompanying spontaneous ether cleavage of the coumaran ring produces a stilbene-type compound, DCA-S. The conversions of DCA-C and DCA-CC are catalyzed by enantiospecific oxidases (PhcC and PhcD) and enantiospecific decarboxylases (PhcF and PhcG), respectively. DCA-S is subjected to cleavage of the interphenyl double bond by lignostilbene ɑ,β-dioxygenase to generate 5-formylferulate and vanillin. Among the eight lignostilbene ɑ,β-dioxygenase genes, vanillate-induced lsdD plays a critical role in cleaving DCA-S. The formyl group of 5-formylferulate is oxidized, and the resultant carboxylic group is subsequently decarboxylated to produce ferulate. Finally, ferulate and vanillin are further catabolized via a previously characterized pathway.