Multiple rotameric states of D390. (a and b) Cartoon representations of OFS_out classes with down (a) and up (b) D390 rotamers. The mesh objects are density maps contoured at 4 σ; only densities within 1.5 Å of labeled residues are displayed for clarity. HP1 is in yellow, and HP2 was removed for clarity. (c) Percentage of particles (total = 1,623,456) that classified into certain D390 rotamers. Numbers in parentheses represent the number of 3-D classes, further detailed in Fig. S9 and Table S6.