Subunits of the HparOR models are colored in a rainbow palette from the N to the C terminus (red); MhraOR5 is colored gray. Structures were compared by Chimera19with the MatchMaker set to identify the best-aligning pair of chains. Superimposition across all fully populated columns in the final alignment: HparOR1 (323 columns, overall RMSD, 2.01 A), HparOR14 (341 columns, overall RMSD, 1.91 A), HparOR16 (325 columns, overall RMSD, 1.90 A), HparOR30 (341 columns, overall RMSD, 2.00 A), HparOR38 (299 columns, overall RMSD, 2.01 A), and HparOR41 (309 columns, overall RMSD, 1.99 A). The RMSD between pruned atom pairs were HparOR1 (1.05 A, 162 atoms; 5.17 A across all 361 pairs), HparOR14 (1.06 A, 190 atoms; 5.40 A across all 365 pairs), HparOR16 (1.30 A, 200 atoms; 3.56 A across all 356 pairs), HparOR30 (1.28 A, 170 atoms; 4.24 A across all 361 pairs), HparOR38 (0.99 A, 162 atoms; 4.82 A across all 371 pairs), and HparOR41 (1.10 A, 177 atoms; 4.60 A across all 355 pairs). The best-aligning chains (S5 or S7b) had RMSD 1.05 0.05 A (mean SEM), whereas the segments analogous to the binding-pocket-forming segments in MhraOR510had RMSD 3.01 0.38 A (S2), 2.61 0.12 A (S3), 3.40 0.46 A (S4), and 1.36 0.09 A (S6). The extracellular loop-2 in MhraOR5, which was unresolved in cryo-EM MhraOR5 structure,10was predicted to have an antiparallel -strand in HparOR14. See alsoFigure S3andVideos S1andS2.
