Presentation: 2025 ND EPSCoR Annual conference 

October 21, 2025, NDSU Memorial Union, Fargo, North Dakota

Investigation of Electron Transfer in Biphenyl Metabolism from Pandorea pnomenusa B-356

Secondary structural elements, cofactor incorporation, and precise positioning of amino acids in electron transfer proteins all play critical roles in modulating electron transfer rates. Cofactors such as flavins and transition metals work in concert with aromatic amino acids like Trp, Phe, Tyr and His which are frequently found in oxidoreductase sequences and often facilitate electron transfer. NADH initiates biphenyl metabolism by transferring two electrons to a FAD containing ferredoxin reductase, BphG. The electrons are then relayed sequentially to a [2Fe-2S] Rieske-type ferredoxin, BphF, which acts as a single electron shuttle to the terminal Rieske Oxygenase BphAE, allowing for regio- and stereo oxidation of the aromatic substrate. In the electron transfer complex formed by the homologous ferredoxin reductase and Rieske ferredoxin from Acidovorax sp strain KKS102, a critical Trp residue serves as a bridge to promote efficient electron transfer. We have determined the high-resolution crystal structures of BphF as well as wild-type and Trp mutant BphG proteins to understand potential atomic rearrangements. Further, we have quantified the electron transfer properties of these proteins using two kinetic assays: reduction of 2,6-Dichloroindophenol to understand direct BphG activity, and reduction of cytochrome c to investigate the transfer of electrons through BphF. This research aims to clarify how specific amino acids can influence the rate of electron transfer between protein partners.