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J. Biol. Chem., Vol. 283, Issue 8, 4841-4849, February 22, 2008

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Sialic Acid Mutarotation Is Catalyzed by the Escherichia coli β-Propeller Protein YjhT^*

Emmanuele Severi, Axel Müller¹, Jennifer R. Potts^¶, Andrew Leech^||, David Williamson^¶, Keith S. Wilson, and Gavin H. Thomas²

From the Department of Biology (Area 10), York Structural Biology Laboratory, Department of Chemistry, ^¶Department of Chemistry and ^||Technology Facility, Department of Biology (Area 15), University of York, York YO10 5YW, United Kingdom

The acquisition of host-derived sialic acid is an important virulence factor for some bacterial pathogens, but in vivo this sugar acid is sequestered in sialoconjugates as the -anomer. In solution, however, sialic acid is present mainly as the β-anomer, formed by a slow spontaneous mutarotation. We studied the Escherichia coli protein YjhT as a member of a family of uncharacterized proteins present in many sialic acid-utilizing pathogens. This protein is able to accelerate the equilibration of the - and β-anomers of the sialic acid N-acetylneuraminic acid, thus describing a novel sialic acid mutarotase activity. The structure of this periplasmic protein, solved to 1.5Å resolution, reveals a dimeric 6-bladed unclosed β-propeller, the first of a bacterial Kelch domain protein. Mutagenesis of conserved residues in YjhT demonstrated an important role for Glu-209 and Arg-215 in mutarotase activity. We also present data suggesting that the ability to utilize -N-acetylneuraminic acid released from complex sialoconjugates in vivo provides a physiological advantage to bacteria containing YjhT.

Received for publication, September 18, 2007 , and in revised form, November 26, 2007.

The atomic coordinates and structure factors (code 2uvk) have been deposited in the Protein Data Bank, Research Collaboratory for Structural Bioinformatics, Rutgers University, New Brunswick, NJ (http://www.rcsb.org/).

^* This work was supported by the Biotechnology and Biological Sciences Research Council. 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.

The on-line version of this article (available at http://www.jbc.org) contains supplemental Experimental Procedures, additional references, Table 1, and Figs. 1, 2, 3, 4, 5, 6, 7, 8.

¹ Present address: Caltech, 157 Broad Center, MC 114-96, Pasadena, CA 91125.

² To whom correspondence should be addressed. Tel.: 44-1904-328678; E-mail: ght2{at}york.ac.uk.

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