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Journal of Bacteriology, April 2008, p. 2903-2910, Vol. 190, No. 8
0021-9193/08/$08.00+0     doi:10.1128/JB.01120-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

RhaU of Rhizobium leguminosarum Is a Rhamnose Mutarotase{triangledown}

Jason S. Richardson,1 Xavi Carpena,2 Jack Switala,1 Rosa Perez-Luque,2 Lynda J. Donald,3 Peter C. Loewen,1 and Ivan J. Oresnik1*

Department of Microbiology, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada,1 Departament de Biologia Estructural (IBMB-CSIC), Institut de Recerca Biomedica (IRB), Parc Científic de Barcelona, Josep Samitier 1-5, 08028 Barcelona, Spain,2 Department of Chemistry, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada3

Received 16 July 2007/ Accepted 11 December 2007

Of the nine genes comprising the L-rhamnose operon of Rhizobium leguminosarum, rhaU has not been assigned a function. The construction of a {Delta}rhaU strain revealed a growth phenotype that was slower than that of the wild-type strain, although the ultimate cell yields were equivalent. The transport of L-rhamnose into the cell and the rate of its phosphorylation were unaffected by the mutation. RhaU exhibits weak sequence similarity to the formerly hypothetical protein YiiL of Escherichia coli that has recently been characterized as an L-rhamnose mutarotase. To characterize RhaU further, a His-tagged variant of the protein was prepared and subjected to mass spectrometry analysis, confirming the subunit size and demonstrating its dimeric structure. After crystallization, the structure was refined to a 1.6-Å resolution to reveal a dimer in the asymmetric unit with a very similar structure to that of YiiL. Soaking a RhaU crystal with L-rhamnose resulted in the appearance of β-L-rhamnose in the active site.

* Corresponding author. Mailing address: Department of Microbiology, University of Manitoba, Winnipeg, MB R3T 2N2, Canada. Phone: (204) 474-7587. Fax: (204) 474-7603. E-mail: oresniki{at}cc.umanitoba.ca

{triangledown} Published ahead of print on 21 December 2007.

Journal of Bacteriology, April 2008, p. 2903-2910, Vol. 190, No. 8
0021-9193/08/$08.00+0     doi:10.1128/JB.01120-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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