The Fur homologue in Borrelia burgdorferi

Borrelia burgdorferi contains a gene that codes for a Fur homologue. The function of this Fur protein is unknown; however, spirochetes grown at 23 or 35°C expressed far as determined by reverse transcriptase PCR. The fùr gene (BB0647) was cloned and overexpressed as a His-Fur fusion protein in Escherichia coli. The fusion protein was purified by zinc-chelate chromatography, and the N-terminal His tag was removed to generate recombinant Fur for use in mobility shift studies. Fur bound DNA containing the E. coli Fur box sequence (GATAATGATAATCATTATC) or Bacillus subtilis Per box sequence (TTATAAT-ATTATAA) with an apparent K_d of ∼ 20 nM. Fur also bound the upstream sequences of three Borrelia genes: BB0646 (gene encoding a hydrolase of the á/β-fold family), BB0647 (fur), and BB0690 (napA). Addition of metal ions was not required. Binding activity was greatly decreased by either exposure to oxidizing agents (H₂O₂, t-butyl hydroperoxide, cumene hydroperoxide, or diamide) or by addition of Zn ²⁺. B. burgdorferi NapA is a homologue of Dps. Dps functions in E. coli to protect DNA against damage during periods of redox stress. Fur may function in B. burgdorferi as a represser and regulate oxidative stress genes. Additional genes (10 chromosomal and 15 plasmid) that may be Fur regulated were identified by in silico analysis.