The olfactory G protein G αolf possesses a lower GDP‐affinity and deactivates more rapidly than G sαshort : consequences for receptor‐coupling and adenylyl cyclase activation

The olfactory G protein G αolf differs from the short splice variant of G sα (G sαS ) in 80 amino acids, but little is known about biochemical differences between G αolf and G sαS . We addressed this question by analyzing fusion proteins of the β 2 ‐adrenoceptor (β 2 AR) and G αolf and G sαS , respectively, using Sf9 insect cells as expression system. The fusion ensured defined receptor/G protein stoichiometry and efficient coupling. High‐affinity agonist binding studies showed that G αolf possesses a lower GDP‐affinity than G sαS As a result, the agonist‐free β 2 AR and the β 2 AR occupied by partial agonists were more efficient at promoting GDP‐dissociation from G αolf than from G sαS a assessed by guanosine 5’‐ O‐ (3‐thiotriphosphate) binding, adenylyl cyclase (AC) activity and GTP hydrolysis. Basal AC activity in the absence of GTP was almost sixfold lower in membranes expressing β 2 AR‐G αolf than in membranes expressing β 2 AR‐G sαS at similar levels, reflecting the lower abundance of G αolf‐GDP relative to G sαS‐GDP . The maximum agonist‐stimulated AC activity with β 2 AR‐G sαS was more than twofold higher than with β 2 AR‐G αolf , but the relative agonist‐stimulation of AC with β 2 AR‐G αolf was much greater than with β 2 AR‐G sαS . The difference in maximum AC activity can be explained by more rapid deactivation of G αolf‐GTP by GTP hydrolysis and GTP dissociation relative to G sαS‐GTP . Taken together, there are biochemical differences between G αolf and G sαS , supporting different roles of these G proteins in vivo .