Comparison of G‐Protein Selectivity of Human 5‐HT 2C and 5‐HT 1A Receptors

A bstract : We compared the ability of human 5‐HT 2C and 5‐HT 1A receptors to couple to selected G proteins expressed in insect Sf9 cells through simultaneous infection with recombinant baculoviruses. We also examined the coupling of G proteins to these same receptors in membranes derived from the Sf9 cells using in situ reconstitution with purified G proteins. Our data show that unoccupied 5‐HT 2C and 5‐HT 1A receptors can attain an activated conformation that is stabilized by interaction with specific G proteins. While high‐affinity agonist binding to the 5‐HT 2C receptor was increased to a greater extent by Gα q than by Gα i2 , the high‐affinity agonist binding to the 5‐HT 1A receptor was preferentially enhanced by Gα i2 coexpression. When the two 5‐HT receptors were expressed in cells also expressing G proteins, both 5‐HT 2C and 5‐HT 1A receptors appear to activate Gα i2 in preference to Gα q . In contrast, in situ reconstitution data show that 5‐HT 2C receptors robustly activate Gα q and marginally activate Gα o or Gα i , whereas 5‐HT 1A receptors only marginally activate Gα q and robustly activate Gα o and Gα i . These results suggest that the overexpression of receptor and potential G‐protein coupling partners in Sf9 cells may lead to erroneous conclusions as to the signaling selectivity of receptors.