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Journal of Bacteriology, September 2006, p. 6135-6142, Vol. 188, No. 17
0021-9193/06/$08.00+0     doi:10.1128/JB.00207-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Evolution of Vitamin B2 Biosynthesis: 6,7-Dimethyl-8-Ribityllumazine Synthases of Brucella

Vanesa Zylberman,1 Sebastián Klinke,1 Ilka Haase,2 Adelbert Bacher,2 Markus Fischer,2* and Fernando Alberto Goldbaum1*

Fundación Instituto Leloir, Buenos Aires, Argentina,1 Lehrstuhl für Organische Chemie und Biochemie Technische Universität München, Lichtenbergstraße 4, D-85748 Garching, Germany2

Received 7 February 2006/ Accepted 7 June 2006

The penultimate step in the biosynthesis of riboflavin (vitamin B2) involves the condensation of 3,4-dihydroxy-2-butanone 4-phosphate with 5-amino-6-ribitylamino-2,4(1H,3H)-pyrimidinedione, which is catalyzed by 6,7-dimethyl-8-ribityllumazine synthase (lumazine synthase). Pathogenic Brucella species adapted to an intracellular lifestyle have two genes involved in riboflavin synthesis, ribH1 and ribH2, which are located on different chromosomes. The ribH2 gene was shown previously to specify a lumazine synthase (type II lumazine synthase) with an unusual decameric structure and a very high Km for 3,4-dihydroxy-2-butanone 4-phosphate. Moreover, the protein was found to be an immunodominant Brucella antigen and was able to generate strong humoral as well as cellular immunity against Brucella abortus in mice. We have now cloned and expressed the ribH1 gene, which is located inside a small riboflavin operon, together with two other putative riboflavin biosynthesis genes and the nusB gene, specifying an antitermination factor. The RibH1 protein (type I lumazine synthase) is a homopentamer catalyzing the formation of 6,7-dimethyl-8-ribityllumazine at a rate of 18 nmol mg–1 min–1. Sequence comparison of lumazine synthases from archaea, bacteria, plants, and fungi suggests a family of proteins comprising archaeal lumazine and riboflavin synthases, type I lumazine synthases, and the eubacterial type II lumazine synthases.

* Corresponding author. Mailing address for Fernando Alberto Goldbaum: Patricias Argentinas 435 (C1405BWE), Buenos Aires, Argentina. Phone: (5411) 5238-7500. Fax: (5411) 5238-7501. E-mail: fgoldbaum{at}leloir.org.ar. Mailing address for Markus Fischer: Lehrstuhl für Organische Chemie und Biochemie, Technische Universität München, Lichtenbergstr. 4, D-85747 Garching, Germany. Phone: 49-89-289-13336. Fax: 49-89-289-13363. E-mail: markus.fischer{at}ch.tum.de.

Journal of Bacteriology, September 2006, p. 6135-6142, Vol. 188, No. 17
0021-9193/06/$08.00+0     doi:10.1128/JB.00207-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.





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