Rigid body models of SUR2A NBD1(A), NBD2 (B) and NBD1/NBD2 (C) under P222 symmetry superimposed on ab initio envelopes. χ2 values are 2.69 for NBD1, 4.09 for NBD2, and 2.86 for NBD1/NBD2. The inside and outside orientations of the octameric ring are denoted in yellow and blue for NBD1, and in green and purple for NBD2, respectively. In the NBD1/NBD2 structure, NBD1 is in yellow and NBD2 in purple. Scattering profiles (purple) from quaternary structure models of NBD1, NBD2 and NBD1/NBD2 were overlaid on experimental scattering curves (black).