Cloning, purification and preliminary X-ray analysis of the C-terminal domain of Helicobacter pylori MotB

The C-terminal domain of MotB ( MotB-C) contains a putative peptidoglycan-binding motif and is believed to anchor the MotA/MotB stator unit of the bacterial flagellar motor to the cell wall. Crystals of Helicobacter pylori MotB-C ( 138 amino-acid residues) were obtained by the hanging-drop vapour-diffusion method using polyethylene glycol as a precipitant. These crystals belong to space group P2(1), with unit-cell parameters a = 50.8, b = 89.5, c = 66.3 angstrom, beta = 112.5 degrees. The crystals diffract X-rays to at least 1.6 angstrom resolution using a synchrotron-radiation source. Self-rotation function and Matthews coefficient calculations suggest that the asymmetric unit contains one tetramer with 222 point-group symmetry. The anomalous difference Patterson maps calculated for an ytterbium-derivative crystal using diffraction data at a wavelength of 1.38 angstrom showed significant peaks on the nu= 1/2 Harker section, suggesting that ab initio phase information could be derived from the MAD data.