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Journal of Bacteriology, October 2005, p. 6936-6942, Vol. 187, No. 20
0021-9193/05/$08.00+0     doi:10.1128/JB.187.20.6936-6942.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Identification of GutQ from Escherichia coli as a D-Arabinose 5-Phosphate Isomerase

Timothy C. Meredith1 and Ronald W. Woodard1,2*

Department of Medicinal Chemistry,1 Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109-10652

Received 14 June 2005/ Accepted 27 July 2005

The glucitol operon (gutAEBDMRQ) of Escherichia coli encodes a phosphoenolpyruvate:sugar phosphotransferase system that metabolizes the hexitol D-glucitol (sorbitol). The functions for all but the last gene, gutQ, have been previously assigned. The high sequence similarity between GutQ and KdsD, a D-arabinose 5-phosphate isomerase (API) from the 3-deoxy-D-manno-octulosonate (KDO)-lipopolysaccharide (LPS) biosynthetic pathway, suggested a putative activity, but its role within the context of the gut operon remained unclear. Accordingly, the enzyme was cloned, overexpressed, and characterized. Recombinant GutQ was shown to indeed be a second copy of API from the E. coli K-12 genome with biochemical properties similar to those of KdsD, catalyzing the reversible aldol-ketol isomerization between D-ribulose 5-phosphate (Ru5P) and D-arabinose 5-phosphate (A5P). Genomic disruptions of each API gene were constructed in E. coli K-12. TCM11[({Delta}kdsD)] was capable of sustaining essential LPS synthesis at wild-type levels, indicating that GutQ functions as an API inside the cell. The gut operon remained inducible in TCM7[({Delta}gutQ)], suggesting that GutQ is not directly involved in D-glucitol catabolism. The conditional mutant TCM15[({Delta}gutQ{Delta}kdsD)] was dependent on exogenous A5P both for LPS synthesis/growth and for upregulation of the gut operon. The phenotype was suppressed by complementation in trans with a plasmid encoding a functional copy of GutQ or by increasing the amount of A5P in the medium. As there is no obvious obligatory role for GutQ in the metabolism of D-glucitol and there is no readily apparent link between D-glucitol metabolism and LPS biosynthesis, it is suggested that A5P is not only a building block for KDO biosynthesis but also may be a regulatory molecule involved in expression of the gut operon.

* Corresponding author. Mailing address: College of Pharmacy, 428 Church St., Ann Arbor, MI 48109-1065. Phone: (734) 764-7366. Fax: (734) 763-2022. E-mail: rww{at}umich.edu.

Journal of Bacteriology, October 2005, p. 6936-6942, Vol. 187, No. 20
0021-9193/05/$08.00+0     doi:10.1128/JB.187.20.6936-6942.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Meredith, T. C., Mamat, U., Kaczynski, Z., Lindner, B., Holst, O., Woodard, R. W. (2007). Modification of Lipopolysaccharide with Colanic Acid (M-antigen) Repeats in Escherichia coli. J. Biol. Chem. 282: 7790-7798 [Abstract] [Full Text]  


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