Crystallographic characterization of a novel protein SixA which exhibits phospho-histidine phosphatase activity in the multistep His-Asp phosphorelay

SixA has been isolated from Escherichia coli as the first protein to exhibi t phospho-histidine phosphatase activity. Recent biochemical studies have s hown that SixA is involved in the signal transduction of the His-Asp phosph orelay through the dephosphorylation of the histidine-containing phosphotra nsfer (HPt) domain of the anaerobic sensor kinase ArcB. Crystals of SixA we re obtained using a hanging-drop vapour-diffusion method with polyethylene glycol and calcium ions. Preliminary X-ray crystallographic analysis reveal ed that the crystals belonged to space group P2(1)2(1)2(1) with unit-cell d imensions a = 39.26, b = 48.62 and c = 83.18 Angstrom, having one molecule in the crystallographic asymmetric unit. The intensity data were collected up to 1.5 Angstrom resolution using synchrotron radiation.