Insight into the metabolism of 1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane (DDT) by biphenyl dioxygenases

Abstract

In this work we have investigated the ability of the biphenyl dioxygenase of Burkholderia xenovorans LB400 (BphAE LB400) and of Pandoraea pnomenusa B356 (BphAE B356) to metabolize DDT. Data show BphAE LB400 is unable to metabolize this substrate but BphAE B356 metabolizes DDT to produce two stereoisomers. Structural analysis of DDT-docked BphAE LB400 and BphAE B356 identified residue Phe336 of BphAE LB400 as critical to prevent productive binding of DDT to BphAE LB400. Furthermore, the fact that residue Gly319 of BphAE B356 is less constrained than Gly321 of BphAE LB400 most likely contributes to the ability of BphAE B356 to bind DDT productively. This was confirmed by examining the ability of BphAE chimeras obtained by shuffling bphA genes from strain B356 and LB400. Chimeras where residues Thr335 (which modulates the constraints on Gly321) and Phe336 (which contacts the substrate) of BphAE LB400 were replaced by Gly and Ile respectively were able to metabolize DDT. However their stereospecificities varied depending on the presence of other segments or residues from BphAE B356. Structural analysis suggests that either one or both of residue 267 and a segments comprised of residue 247–260 are likely involved in stereospecificity.