Remarkable Ability of Pandoraea pnomenusa B356 Biphenyl Dioxygenase To Metabolize Simple Flavonoids

摘要

Many investigations have provided evidence that plant secondary metabolites, especially flavonoids, may serve as signal molecules to trigger the abilities of bacteria to degrade chlorobiphenyls in soil. However, the bases for this interaction are largely unknown. In this work, we found that BphAE_(B356), the biphenyl/chlorobiphenyl dioxygenase from Pandoraea pnomenusa B356, is significantly better fitted to metabolize flavone, isoflavone, and flavanone than BphAE_(LB400) from Burkholderia xenovorans LB400. Unlike those of BphAE_(LB400), the kinetic parameters of BphAE_(B356) toward these flavonoids were in the same range as for biphenyl. In addition, remarkably, the biphenyl catabolic pathway of strain B356 was strongly induced by isoflavone, whereas none of the three flavonoids induced the catabolic pathway of strain LB400. Docking experiments that replaced biphenyl in the biphenyl-bound form of the enzymes with flavone, isoflavone, or flavanone showed that the superior ability of BphAE_(B356) over BphAE_(LB400) is principally attributable to the replacement of Phe336 of BphAE_(LB400) by Ile334 and of Thr335 of BphAE_(LB400) by Gly333 of BphAE_(B356). However, biochemical and structural comparison of BphAE_(B356) with BphAE_( p4 ), a mutant of BphAE_(LB400) which was obtained in a previous work by the double substitution Phe336Met Thr335Ala of BphAE_(LB400), provided evidence that other residues or structural features of BphAE_(B356) whose precise identification the docking experiment did not allow are also responsible for the superior catalytic abilities of BphAE_(B356). Together, these data provide supporting evidence that the biphenyl catabolic pathways have evolved divergently among proteobacteria, where some of them may serve ecological functions related to the metabolism of plant secondary metabolites in soil.