Two-step purification of outer membrane proteins.

Here, we describe a simple and efficient method for the purification of Escherichia coli outer membrane proteins. We have tested this protocol for the purification of Wza and Osmoporin C (OmpC) proteins. Both proteins were purified to homogeneity, in two steps, by anion exchange and size exclusion chromatography with a final yield of 92.5 mg for the Wza protein and 291.5 mg for the OmpC protein. The purity of the samples was judged by electrophoretic analysis, mass spectrometry, single particle analysis, three-dimensional (3D) crystallisation and X-ray diffraction.