Purification, crystallization and preliminary X-ray diffraction studies of recombinant class A non-specific acid phosphatase of Salmonella typhimurium

The phoN gene of Salmonella enterica sv. Typhimurium strain MD6001 was cloned in the multicopy plasmid pBluescript SK-. The nucleotide sequence of the cloned gene differs from the corresponding S. typhimurium LT2 sequence at 23 residues, leading to 15 amino-acid differences, but was very close to the S. typhi phoN sequence (only three nucleotide and two amino-acid differences). The recombinant PhoN protein was purified to homogeneity. Two forms of crystals were harvested from a single crystallization condition. Diffraction intensity data were collected using a laboratory X-ray source to resolution limits of 2.5 and 2.8 Angstrom for crystals belonging to space group C2 and C222(1), respectively. Based on noncrystallographic symmetry, four monomers of PhoN are expected to be present in the asymmetric unit of the C2 unit cell. Two monomers of a biologically active dimer in the asymmetric unit of the C222(1) unit cell are expected from the Matthews coefficient.