Preliminary X-ray crystallographic studies on the Helicobacter pylori ABC transporter glutamine-binding protein GlnH

Periplasmic binding proteins (PBPs) of Gram-negative bacteria sense essential nutrients and mediate their uptake by ATP-binding cassette (ABC) transporters. The gene for a PBP of H. pylori SS1, annotated as GlnH, is located within the glnPQH operon encoding an ABC importer system. In this study, GlnH has been expressed in E. coli and purified to > 98% homogeneity. The recombinant protein was folded according to the circular dichroism (CD) analysis and behaved as a monomer in solution. Crystals of GlnH have been grown by the hanging-drop vapour-diffusion method using polyethylene glycol (PEG) 4000 as a precipitating agent. The crystals belonged to the primitive monoclinic space group P21 with unit cell parameters a = 38.67, b = 93.36, c = 64.13 Å, β = 93.72°. A complete X-ray diffraction data set was collected to 1.3 Å resolution from a single crystal using synchrotron radiation. Molecular replacement using this data revealed that the asymmetric unit contains a single molecule. This is a key step towards elucidation of the structural basis of the GlnH function.