Cloning, expression, purification and crystallization of an endotoxin-biosynthesis enzyme from Neisseria meningitidis

The enzyme phosphoethanolamine transferase A is involved in the addition of phosphoethanolamine moieties to lipid A in Neisseria meningitidis. The enzyme is composed of an N-terminal transmembrane domain and a C-terminal soluble domain that is present in the periplasm of the bacteria. A membrane-deletion construct of the enzyme was designed and expressed in Escherichia coli. Well ordered crystals that diffracted to 1.7 Å resolution were obtained by carrying out a limited trypsin digestion of the protein to remove a predicted N-terminal disordered portion. The crystals belonged to space group P2(1), with unit-cell parameters a=44.3, b=71.6, c=49.9 Å, β=109.2°, and contained one molecule in the asymmetric unit.