Cloning, purification, crystallization and preliminary X-ray analysis of DOS heme domain, a new heme oxygen sensor in Escherichia coli

The heme-containing PAS domain of the direct oxygen-sensor protein (DOSH), a bona fide oxygen-sensor protein, has been cloned from Escherichia coli strain K12 and successfully purified. The oxidized form of this protein was crystallized by the hanging-drop method with a PEG 8000-based precipitant. Preliminary X-ray diffraction studies of the PAS-domain crystal show that it belongs to the orthorhombic space group P212121, with unit-cell parameters a = 46.1, b = 68.1, c = 82.6 A. A complete diffraction data set was collected to 1.9 A for MAD phasing. The electron-density map shows two molecules in an asymmetric unit and a unique six-coordination of the heme iron.