Manipulating phospholipids for crystallization of membrane transport proteins

One of the major bottlenecks in obtaining x‐ray structures of membrane proteins is crystallization. By applying an established crystallization protocol for the lactose permease of Escherichia coli (LacY), a systematic study of the effects of phospholipids on crystallization was undertaken. We observe that hexagonal, tetragonal or orthorhombic crystals, which diffract quite differently, correlate with the concentration of phospholipids that co‐purify with the protein. Correspondingly, addition of E. coli phospholipids at increasing concentrations to LacY samples that were de‐lipidated leads to different crystal forms. Two structures of C154G LacY were obtained by carefully adjusting the membrane protein to detergent ratio during solubilization. Furthermore, wild‐type LacY, a particularly difficult protein, was crystallized by using this approach. Thus, it is likely that manipulation of phospholipids during crystallization is a good general strategy for membrane proteins.