LsdD has a critical role in the dehydrodiconiferyl alcohol catabolism among eight lignostilbene α,β-dioxygenase isozymes in Sphingobium sp. strain SYK-6

Abstract

Lignin is the most abundant aromatic bioresource in nature, and elucidation of its biodegradation system is essential for understanding the carbon cycling on earth and its effective usage. The β−5 bond is one of the intermolecular linkages in lignin. Sphingobium sp. strain SYK-6 can assimilate various lignin-derived aromatic compounds, including a β−5 bond-containing dimer (phenylcoumaran-type), dehydrodiconiferyl alcohol (DCA). In the catabolic pathway of DCA, a stilbene-type compound, 3-(4-hydroxy-3-(4-hydroxy-3-methoxystyryl)-5-methoxyphenyl)acrylate (DCA-S), is produced. DCA-S is subjected to the cleavage of the interphenyl double bond by lignostilbene α,β-dioxygenase (LSD) to generate 5-formylferulate and vanillin. Among the eight LSD genes (lsdA−lsdH) found in the SYK-6 genome, the gene products of lsdA, lsdC, lsdD, and lsdG exhibited DCA-S conversion activity. The DCA-S conversion activity of SYK-6 was induced (6.8-fold) by vanillate produced as an intermediate metabolite of DCA-S. Of the LSD genes mentioned above, only the transcriptions of lsdA, lsdD, and lsdG were induced (2.6–10-fold) in the presence of vanillate. Analyses of lsdA, lsdD, and lsdG mutants showed that an lsdD mutant lost the DCA-S conversion activity under vanillate-induced conditions. These results demonstrate that lsdD plays a critical role in converting DCA-S during the DCA catabolism in SYK-6.