Crystal packing in MdfA crystals. Packing arrangements of (a) the transporter (MdfA-VD), (b, c) the MdfA–YN1074 complex within vapour-diffusion-grown (MdfA–YN1074-VD) crystals and (d, e) the MdfA–YN1074 membrane-protein complex within lipidic cubic phase-grown crystals (MdfA–YN1074-LCP). Selected symmetry-element symbols are shown for orientation. (a) The two MdfA monomers (green, cyan) within the asymmetric unit of MdfA-VD align to form infinite superhelical chains (dotted line) that are stabilized by lateral hydrophobic contacts. Individual chains contact each other via a small number of hydrophilic contacts. View parallel to the crystallographic a axis. (b) Crystal contacts in MdfA–YN1074-VD are dominated by interactions between the Fabs (yellow, pink) from symmetry-related molecules. Within the lattice, the molecules are arranged in rippled layers (dotted line), with major contacts between the layers provided by the Fabs. The view is parallel to the crystallographic a axis. (c) One layer from (b), viewed parallel to the crystallographic b axis. (d) In the MdfA–YN1074-LCP crystals, MdfA (green; for clarity, twofold symmetry-related molecules are shown in cyan, although these are crystallographically equivalent) is found in a two-dimensional membrane-like array. MdfA layers sandwich those of the Fab YN1074 (yellow; pink), resulting in a favourable segregation of hydrophobic and hydrophilic crystal contacts. The view is parallel to the crystallographic a axis. (e) The MdfA layer from (d), viewed parallel to the crystallographic c axis.