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Proc Natl Acad Sci U S A. 2014 Dec 16;111(50):17815-20. doi: 10.1073/pnas.1414622111. Epub 2014 Dec 1.

Erythritol feeds the pentose phosphate pathway via three new isomerases leading to D-erythrose-4-phosphate in Brucella.

Author information

1
Research Unit in Microorganisms Biology, University of Namur, B-5000 Namur, Belgium;
2
Welbio and de Duve Institute, Université Catholique de Louvain, B-1200 Brussels, Belgium;
3
Departamento de Microbiología e Instituto de Salud Tropical, Universidad de Navarra, 31008 Pamplona, Spain;
4
Institute of Biochemical Engineering, Technische Universität Braunschweig, 38106 Braunschweig, Germany; and.
5
Institute of Systems Biotechnology, Saarland University, 66123 Saarbrücken, Germany.
6
Welbio and de Duve Institute, Université Catholique de Louvain, B-1200 Brussels, Belgium; emile.vanschaftingen@uclouvain.be jean-jacques.letesson@unamur.be.
7
Research Unit in Microorganisms Biology, University of Namur, B-5000 Namur, Belgium; emile.vanschaftingen@uclouvain.be jean-jacques.letesson@unamur.be.

Abstract

Erythritol is an important nutrient for several α-2 Proteobacteria, including N2-fixing plant endosymbionts and Brucella, a worldwide pathogen that finds this four-carbon polyol in genital tissues. Erythritol metabolism involves phosphorylation to L-erythritol-4-phosphate by the kinase EryA and oxidation of the latter to L-3-tetrulose 4-phosphate by the dehydrogenase EryB. It is accepted that further steps involve oxidation by the putative dehydrogenase EryC and subsequent decarboxylation to yield triose-phosphates. Accordingly, growth on erythritol as the sole C source should require aldolase and fructose-1,6-bisphosphatase to produce essential hexose-6-monophosphate. However, we observed that a mutant devoid of fructose-1,6-bisphosphatases grew normally on erythritol and that EryC, which was assumed to be a dehydrogenase, actually belongs to the xylose isomerase superfamily. Moreover, we found that TpiA2 and RpiB, distant homologs of triose phosphate isomerase and ribose 5-phosphate isomerase B, were necessary, as previously shown for Rhizobium. By using purified recombinant enzymes, we demonstrated that L-3-tetrulose-4-phosphate was converted to D-erythrose 4-phosphate through three previously unknown isomerization reactions catalyzed by EryC (tetrulose-4-phosphate racemase), TpiA2 (D-3-tetrulose-4-phosphate isomerase; renamed EryH), and RpiB (D-erythrose-4-phosphate isomerase; renamed EryI), a pathway fully consistent with the isotopomer distribution of the erythrose-4-phosphate-derived amino acids phenylalanine and tyrosine obtained from bacteria grown on (13)C-labeled erythritol. D-erythrose-4-phosphate is then converted by enzymes of the pentose phosphate pathway to glyceraldehyde 3-phosphate and fructose 6-phosphate, thus bypassing fructose-1,6-bisphosphatase. This is the first description to our knowledge of a route feeding carbohydrate metabolism exclusively via D-erythrose 4-phosphate, a pathway that may provide clues to the preferential metabolism of erythritol by Brucella and its role in pathogenicity.

KEYWORDS:

Brucella; alphaproteobacteria; erythritol; pentose phosphate cycle; tetrose metabolism

PMID:
25453104
PMCID:
PMC4273404
DOI:
10.1073/pnas.1414622111
[Indexed for MEDLINE]
Free PMC Article

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