Figure 5.

TM5 and TM6 are responsible for G_s and G_i selectivity. A) Representative of the TM5/TM6 structural geometry of G_s‐coupled receptors. B) Representation of the TM5/TM6 structural geometry of G_i‐coupled receptors. C) Violin plots depicting four distinct features of TM5/TM6 in G_s‐ and G_i/o‐coupled receptors. The white dot denotes the median. The interquartile range is shown by the broad black bar in the middle. Except for points considered to be “outliers” using an interquartile range‐based technique, the thin line reflects the remainder of the distribution. n = 54, ^ns P > 0.05, *P < 0.05, **P < 0.01 by Mann‐Whitney U test. D) Schematic representation of the “TM5/TM6 swap” experiments. E–F) Dose‐dependent curves for histamine induced G‐protein dissociation and cAMP accumulation in HEK293 cells expressing chimera receptors (n  = 3). E) Replacement of I^5.56‐F^6.44 of H₂R with F^5.56‐F^6.44 of H₃R did not confer the ability to dissociate G_i‐protein (left), but resulted in loss of the ability to activate the G_s signal pathway (right). F) Replacement of P^5.50‐P^6.50 of H₃R with P^5.50‐P^6.50 of H₂R resulted in gain of the ability to activate the G_s signal pathway (left), but loss of the ability to dissociate G_i‐protein (right).