Electron density. (A) Electron density of TM 10. The 2mFo-DFc map shown in blue (contoured at 1.5 σ) was calculated with phases derived from the model before reassigning the sequence of TM 10 (shown) and averaged over the four molecules of the asymmetric unit. The anomalous difference map shown in red has been calculated from the selenomethionine-derivatized triple mutant and contoured at 3.6 σ. (B) The same maps as in A but with the structure of the wild-type protein (refined before the data of the triple mutant were collected). (C) Stereo view of the superposition of the final refined structure of the triple mutant (green) on that of the published monomeric structure (gray) (Hunte et al., 2005). The anomalous difference map is shown as in A. Met296 is in cyan, and Leu296 from the published structure is in wine red. Overall, there is good correspondence in the position of the helices and methionines between the two structures, in agreement with the similar activity of the mutant to wild type (Fig. 4). An enlarged view of TM 10 is shown in Fig. S1.