Fig. 9: Determinants of Gs and Gi/o coupling differences between HRs.

a Cartoon and surface representation of the binding area of H2R (left panel), H3R (middle panel), and H4R (right panel) with their respective coupled Gα subunits. Residues within 4.5 Å of H2R or H3R in Gαs or Gαi are highlighted in wheat or salmon, respectively. b Comparison of residues between agonist-bound H2R, H3R, or H4R that contact their corresponding downstream G protein subtypes, Gαs, Gαi, or Gαo, respectively. Residues of HRs that show common interaction with Gs or Gi/o are indicated by cyan circles, residues showing unique interaction with Gs are indicated by orange circles, residues showing unique interaction with Gi/o are indicated by purple circles, and residues that show no interaction with G proteins are depicted as white circles. Residue positions with Ballesteros–Weinstein numbers are shown as superscripts for H2R, H3R, or H4R on the top of the scheme. c Structural comparison of the TM5–TM6 regions of H2R (olive drab), H3R (medium slate blue), and H4R (dark cyan) structures. d Representative concentration-dependent response curves of H3R and H4R, along with their R^34.54A, F^6.25A and R^6.29A mutants, in response to histamine/Proxyfan (H3R) and histamine/Immepip (H4R) using the Gαi-Gγ dissociation assay. The pEC50 and E_max values are provided in Supplementary Table 6. Data from three independent experiments are presented as the mean ± SEM (n = 3).