Purification, crystallization and preliminary crystallographic analysis of the periplasmic binding protein ProX from Escherichia coli

A periplasmic binding protein (ProX) for the compatible solutes glycine betaine and proline betaine from Escherichia coli was crystallized using the hanging-drop vapour-diffusion method. Crystals were grown using a protein concentration of 10 mg ml^-1 and a precipitant of 26-28% PEG 4000 in 50 mM PIPES pH 6.2-6.4. Native diffraction data to 1.93 Å resolution have been obtained from crystals at 290 K. The crystals belong to the space group P2₁2₁2₁, with unit-cell parameters a = 48.1, b = 55.0, c = 115.7 Å, and contain one molecule per asymmetric unit.