Purification, crystallization and preliminary X-ray crystallographic analysis of the outer membrane lipoprotein NlpE from Escherichia coli

The outer membrane lipoprotein NlpE functions in stress response by activating the Cpx signal transduction pathway. The nonlipidated Cys1Ala mutant of NlpE with a C-terminal His tag from Escherichia coli was constructed, overexpressed and purified. Crystals of NlpE were grown in two distinct forms by the sitting-drop vapour-diffusion method at 298 K. The tetragonal crystals diffracted to 2.8 A resolution and belong to space group P43212. The monoclinic crystals diffracted to 3.0 A resolution and belong to space group C2. Initial phases were obtained from a tetragonal crystal of selenomethionylated protein by the MAD method.