Potential Electron Transfer Protein Complexes During the Initiation of Polychlorinated Biphenyl Degradation Investigated by Small‐Angle X‐ray Scattering

Abstract

The first step in the oxidative degradation of the persistent environmental pollutants polychlorinated biphenyls (PCBs) by the aerobic microbe Pandoraea pnomenusa B‐356 is the stereo‐ and regio‐selective insertion of both atoms from molecular oxygen into the aromatic substrate to form a cis‐dihydrodiol. This reaction is catalyzed by biphenyl 2,3‐dioxygenase (BPDO), Rieske Oxygenase containing a Rieske 2Fe‐2S cluster and a catalytic mononuclear Fe2+ atom. Electrons, required to activate molecular oxygen during hydroxylation of the aromatic substrate, are transferred to BPDO from NADH via a short electron transfer chain consisting of a FAD‐dependent ferredoxin reductase (BphG) and a 2Fe‐2S cluster containing Rieske‐type ferredoxin (BphF). To understand the solution characteristics of the potential electron transfer complexes, we performed size exclusion chromatography coupled with small‐angle X‐ray scattering (SEC‐SAXS) to determine the molecular envelopes of BphG in complex with BphF, as well as BphF in complex with BPDO. These envelopes are compared to the current crystallographic model of BphA3:BphA4 from Acidovorax sp. strain KKS102 and our predicted model for BphF:BPDO. These observations provide insights into the protein‐protein associations for intermolecular electron transfer during the initiation of PCB biodegradation.Support or Funding InformationFunded by NSF ND EPSCoR DDA #FAR0025216 to JLJ; NIH NINDS 1R03 NS090939 and NSF MCB‐1413525 to SCS; NIH NIGMS 1R15 GM113227, NIH NCRR 2P20 RR015566, and NIH NIGMS P30 GM103332 to CLC.