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Journal of Bacteriology, May 2006, p. 3498-3506, Vol. 188, No. 10
0021-9193/06/$08.00+0     doi:10.1128/JB.188.10.3498-3506.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

WrbA from Escherichia coli and Archaeoglobus fulgidus Is an NAD(P)H:Quinone Oxidoreductase

Eric V. Patridge and James G. Ferry*

Department of Biochemistry and Molecular Biology, Eberly College of Science, The Pennsylvania State University, 205 South Frear Laboratory, University Park, Pennsylvania 16802-4500

Received 19 December 2005/ Accepted 6 March 2006

WrbA (tryptophan [W] repressor-binding protein) was discovered in Escherichia coli, where it was proposed to play a role in regulation of the tryptophan operon; however, this has been put in question, leaving the function unknown. Here we report a phylogenetic analysis of 30 sequences which indicated that WrbA is the prototype of a distinct family of flavoproteins which exists in a diversity of cell types across all three domains of life and includes documented NAD(P)H:quinone oxidoreductases (NQOs) from the Fungi and Viridiplantae kingdoms. Biochemical characterization of the prototypic WrbA protein from E. coli and WrbA from Archaeoglobus fulgidus, a hyperthermophilic species from the Archaea domain, shows that these enzymes have NQO activity, suggesting that this activity is a defining characteristic of the WrbA family that we designate a new type of NQO (type IV). For E. coli WrbA, the KmNADH was 14 ± 0.43 µM and the Kmbenzoquinone was 5.8 ± 0.12 µM. For A. fulgidus WrbA, the KmNADH was 19 ± 1.7 µM and the Kmbenzoquinone was 37 ± 3.6 µM. Both enzymes were found to be homodimeric by gel filtration chromatography and homotetrameric by dynamic light scattering and to contain one flavin mononucleotide molecule per monomer. The NQO activity of each enzyme is retained over a broad pH range, and apparent initial velocities indicate that maximal activities are comparable to the optimum growth temperature for the respective organisms. The results are discussed and implicate WrbA in the two-electron reduction of quinones, protecting against oxidative stress.

* Corresponding author. Mailing address: Department of Biochemistry and Molecular Biology, Eberly College of Science, The Pennsylvania State University, 205 South Frear Laboratory, University Park, PA 16802-4500. Phone: (814) 863-5721. Fax: (814) 863-6217. E-mail: jgf3{at}psu.edu.

Journal of Bacteriology, May 2006, p. 3498-3506, Vol. 188, No. 10
0021-9193/06/$08.00+0     doi:10.1128/JB.188.10.3498-3506.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



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