Overexpression, purification, crystallization and preliminary X-ray crystallographic characterization of the receiver domain of the response regulator PhoP from Enterococcus faecalis ATCC 29212

Phosphate (Pho) regulon plays a critical role in bacterial phosphate homeostasis. It is regulated by two-component system (TCS) that comprises a sensor histidine kinase and transcriptional response regulator (RR). PhoP from Enterococcus faecalis (EfPhoP) belongs to the OmpR subfamily of RRs. It has not yet been structurally characterized because it is difficult to crystallize it to full-length form. In this study, a truncated form of EfPhoP containing the receiver domain (EfPhoP-RD) was constructed, purified to homogeneity and crystallized using the hanging-drop vapour-diffusion method. The crystal of EfPhoP-RD diffracted to 3.5 A resolution and belonged to the orthorhombic space group C2221, with unit-cell parameters a = 118.74, b = 189.83, c = 189.88 A. The asymmetric unit contains approximately 12 molecules, corresponding to a Matthews coefficient (Vm) of 2.50 A3 Da−1 with a solvent content of 50.9%.