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J. Biol. Chem., Vol. 280, Issue 34, 30100-30106, August 26, 2005

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Scission of the Lactyl Ether Bond of N-Acetylmuramic Acid by Escherichia coli "Etherase"^*

Tina Jaeger, Momo Arsic, and Christoph Mayer¶

From the Fachbereich Biologie, Microbiology und Molecular Toxicology, University of Konstanz, 78457 Konstanz, Germany

The ubiquitous bacterial cell wall sugar N-acetylmuramic acid (MurNAc) carries a unique D-lactyl ether substituent at the C3 position. Recently, we proposed an etherase capable of cleaving this lactyl ether to be part of the novel bacterial MurNAc dissimilation pathway (Dahl, U., Jaeger, T., Nguyen, B. T., Sattler, J. M., Mayer, C. (2004) J. Bacteriol. 186, 2385–2392). Here, we report the identification of the first known MurNAc etherase. The encoding gene murQ is located at 55 min on the Escherichia coli chromosome adjacent to murP, the MurNAc-specific phosphotransferase system. A murQ deletion mutant could not grow on MurNAc as the sole source of carbon and energy but could be complemented by expressing murQ from a plasmid. The mutant had no obvious phenotype when grown on different carbon sources but accumulated MurNAc 6-phosphate at millimolar concentrations from externally supplied MurNAc. Purified MurQ-His₆ fusion protein and extracts of cells expressing murQ both catalyze the cleavage of MurNAc 6-phosphate, with GlcNAc 6-phosphate and D-lactate being the primary products. The ¹⁸O label from enriched water is incorporated into the sugar molecule, showing that the C3–O bond is cleaved and reformed by the enzyme. Moreover, an intermediate was detected and identified as an unsaturated sugar molecule. Based on this observation, we suggested a lyase-type mechanism (-elimination/hydration) for the cleavage of the lactyl ether bond of MurNAc 6-phosphate. Close homologs of murQ were found on the chromosome of several bacteria, and amino acid sequence similarity with the N-terminal domain of human glucokinase-regulatory protein (GckR or GKRP) was recognized.

Received for publication, February 28, 2005 , and in revised form, June 27, 2005.

^* This work was supported by a grant from the Deutsche Forschungsgemeinschaft (DFG Project MA2436/1). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

This work is dedicated to Dr. Hubert Mayer in honor of his 75th birthday.

^¶ To whom correspondence should be addressed: Fachbereich Biologie, University of Konstanz, 78457 Konstanz, Germany. Tel.: 49-7531-88-4854; Fax: 49-7531-88-3356; E-mail: ch.mayer{at}uni-konstanz.de.

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