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

In this work we have investigated the ability of the biphenyl dioxygenase of Burkholderia xenovorans LB400 (BphAELB400) and of Pandoraea pnomenusa B356 (BphAEB356) to metabolize DDT. Data show BphAELB400 is unable to metabolize this substrate but BphAEB356 metabolizes DDT to produce two stereoisomers. Structural analysis of DDT-docked BphAELB400 and BphAEB356 identified residue Phe336 of BphAELB400 as critical to prevent productive binding of DDT to BphAELB400. Furthermore, the fact that residue Gly319 of BphAEB356 is less constrained than Gly321 of BphAELB400 most likely contributes to the ability of BphAEB356 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 BphAELB400 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 BphAEB356. Structural analysis suggests that either one or both of residue 267 and a segments comprised of residue 247–260 are likely involved in stereospecificity.