The Boredetella
pertussis wlbD gene product is a putative uridine-5-diphosphate
N-acetylglucosamine (
UDP-GlcNAc) 2'-epimerase involved in Band A
lipopolysaccharide biosynthesis. The wlbD gene is homologous to Escherichia coli rffE (32% identical), an established
UDP-GlcNAc 2'-epimerase that is involved in
enterobacterial common antigen (ECA) formation. The structure of the rffE
protein reveals an unexpected role for a bound
sodium ion in orientating a substrate-binding alpha-helix in the
enzyme active site. Whilst key active-site residues in rffE are present in the wlbD sequence, the
sodium-binding residues outside the active site are absent. This raises questions about the modulation of
enzyme activity in these two
enzymes. The wlbD gene from B.
pertussis has been cloned and overexpressed in E. coli and the resulting
protein has been purified to homogeneity. In the current study, crystals of the mutant Gln339Arg wlbD
enzyme have been obtained by sitting-drop vapour diffusion. Uncomplexed Gln339Arg and
UDP-GlcNAc complex data sets have been collected in-house on a rotating-
anode generator to 2.1 A. Combined, the data sets identify the space group as P2(1)2(1)2(1), with unit-cell parameters a = 78, b = 91, c = 125 A, alpha = beta = gamma = 90 degrees. The asymmetric unit contains two monomers and 53%
solvent.