Crystallization and preliminary diffraction studies of native and selenomethionine CcmG (CycY, DsbE)

Disulfide-bond (Dsb) proteins are a family of redox proteins containing a Cys-X-X-Cys motif. They are essential for disulfide-bond exchange in the bacterial periplasm and are necessary for the correct folding and function of many secreted proteins. CcmG (DsbE) is a reducing Dsb protein required for cytochrome c maturation. Crystals of Bradyrhizobium japonicum CcmG have been obtained that diffract X-rays to 1.14 Å resolution. The crystals are orthorhombic, space group P2₁2₁2₁, with unit-cell parameters a = 35.1, b = 48.2, c = 90.2 Å. Selenomethionine CcmG was expressed without using a methionine auxotroph or methionine-pathway inhibition and was purified without reducing agents.