Purification, crystallization and preliminary crystallographic studies of an integral membrane protein, cytochrome bo₃ ubiquinol oxidase from Escherichia coli

Cytochrome bo₃ ubiquinol oxidase has been successfully purified for crystallization. Single crystals of this integral membrane protein diffract X-rays to 3.5 Å resolution and belong to the orthorhombic space group C222₁. From the diffraction data, the unit-cell parameters were determined to be a = 91.3, b = 370.3, c = 232.4 Å. The crystals have a solvent content of 59% and contain two molecules per asymmetric unit. A search model generated from the structures of cytochrome c oxidase from Paracoccus denitrificans and the extrinsic domain of cytochrome bo₃ ubiquinol oxidase from Escherichia coli was used for molecular-replacement studies, resulting in a solution with sensible molecular packing.