Chapter 6: Structure Determination at Low-resolution, Anisotropic Data and Crystal Twinning

NorM from Neisseria gonorrhoeae (NorM-NG) belongs to the Multidrug And Toxic compound Extrusion (MATE) family of membrane transport proteins, which can extrude cytotoxic chemicals across cell membranes and confer multidrug resistance. Here, we describe the structure determination of NorM-NG, which had been hampered by low resolution (∼4 Å), data anisotropy and pseudo-merohedral twinning. The crystal structure was solved by using molecular replacement and corroborated by conducting difference Fourier analysis. The NorM-NG structure displays an extracellular-facing conformation, similar to that of NorM-NG bound to a crystallization chaperone. The approaches taken to determining the NorM-NG structure and the lessons learned from this study are discussed, which may be useful for analyzing X-ray diffraction data with similar shortcomings.