Expression, crystallization and preliminary X-ray crystallographic studies of the outer membrane protein OmpW from Escherichia coli

OmpW is an eight-stranded 21 kDa molecular-weight beta-barrel protein from the outer membrane of Gram-negative bacteria. It is a major antigen in bacterial infections and has implications in antibiotic resistance and in the oxidative degradation of organic compounds. OmpW from Escherichia coli was cloned and the protein was expressed in inclusion bodies. A method for refolding and purification was developed which yields properly folded protein according to circular-dichroism measurements. The protein has been crystallized and crystals were obtained that diffracted to a resolution limit of 3.5 angstrom. The crystals belong to space group P422, with unit- cell parameters a = 122.5, c = 105.7 angstrom. A homology model of OmpW is presented based on known structures of eight-stranded beta-barrels, intended for use in molecular-replacement trials.