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Bystrom, Liam

University of British Columbia

Fusobacterium nucleatum is a Gram-negative obligate anaerobe and a normal constituent of the human oral cavity. Additionally, F. nucleatum can disseminate through the bloodstream of its host and colonize distal sites including tumors of the colon where it can exacerbate disease. In the host, F. nucleatum encounters oxygen as well as derivative reactive oxygen and nitrogen species, but there is limited information on oxidative and nitrosative defense mechanisms present in F. nucleatum. Examination of F. nucleatum subsp. polymorphum’s genome revealed the presence of a putative flavodiiron protein (FDP) which is known to reduce O₂ and/or NO to H₂O or N₂O, respectively. Colocalized with the FDP gene is a gene encoding a multicomponent enzyme called butyryl-CoA reductase (BCR). BCR contains three distinct domains: butyryl-CoA dehydrogenase (BCD), the C-terminal domain of the α-subunit of an electron transfer flavoprotein (ETFα), and rubredoxin (Rd). This thesis details work which shows that BCR functions to oxidize butyryl-CoA and transfer the reducing equivalents to the FDP for reduction of O₂ to H₂O. Electron transfer is dependent on the formation of a neutral semiquinone of the FAD bound to BCD and an anionic semiquinone of the FAD bound to ETFα. This enzyme pair gives F. nucleatum the ability to use a common metabolite (butyryl-CoA) with a high reduction potential to reduce O₂ and prevent oxidative stress. By using butyryl-CoA as reductant, F. nucleatum can derive additional energy from its amino acid-based metabolism while simultaneously removing toxic O₂. The novel BCR-FDP is one of the only enzymes characterized from F. nucleatum to function in oxidative stress defense, making it a potentially critical enzyme for F. nucleatum’s survival and subsequent infection. Bioinformatic analysis revealed that BCR-FDP is prevalent in many species of anaerobic gut bacteria where it may function in maintaining anaerobiosis and therefore a healthy gut microbiome.

Text

2024-11-18

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/89672

Biochemistry and Molecular Biology

University of British Columbia

UBCO

http://creativecommons.org/licenses/by-nc-nd/4.0/