title: RhaU of Rhizobium leguminosarum is a rhamnose mutarotase.
abstract: 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-A 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 beta-L-rhamnose in the active site.
authors.affiliation: Department of Microbiology, University of Manitoba, Winnipeg, MB R3T 2N2, Canada.
authors.forename: Jason S
authors.initials: JS
authors.lastname: Richardson
authors.forename: Xavi
authors.initials: X
authors.lastname: Carpena
authors.forename: Jack
authors.initials: J
authors.lastname: Switala
authors.forename: Rosa
authors.initials: R
authors.lastname: Perez-Luque
authors.forename: Lynda J
authors.initials: LJ
authors.lastname: Donald
authors.forename: Peter C
authors.initials: PC
authors.lastname: Loewen
authors.forename: Ivan J
authors.initials: IJ
authors.lastname: Oresnik
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D001483:Base Sequence; D001665:Binding Sites; D002238:Carbohydrate Epimerases / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D018360:Crystallography, X-Ray; D019281:Dimerization; D029968:Escherichia coli Proteins / Q000235:genetics; D017353:Gene Deletion; D005990:Glycerol / Q000378:metabolism; D013058:Mass Spectrometry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D020836:Protein Structure, Quaternary; D012210:Rhamnose / Q000378:metabolism*; D016961:Rhizobium leguminosarum / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D017386:Sequence Homology, Amino Acid
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D002238:Carbohydrate Epimerases; C501328:rhamnose mutarotase, E coli; C019646:aldose 1-epimerase; D005990:Glycerol; D012210:Rhamnose