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

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Abstract
The olfactory G protein Gαolf differs from the short splice variant of Gsα (GsαS) in 80 amino acids, but little is known about biochemical differences between Gαolf and GsαS. We addressed this question by analyzing fusion proteins of the β2‐adrenoceptor (β2AR) and Gαolf and GsαS, 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 Gαolf possesses a lower GDP‐affinity than GsαS As a result, the agonist‐free β2AR and the β2AR occupied by partial agonists were more efficient at promoting GDP‐dissociation from Gαolf than from GsαS 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 β2AR‐Gαolf than in membranes expressing β2AR‐GsαS at similar levels, reflecting the lower abundance of Gαolf‐GDP relative to GsαS‐GDP. The maximum agonist‐stimulated AC activity with β2AR‐GsαS was more than twofold higher than with β2AR‐Gαolf, but the relative agonist‐stimulation of AC with β2AR‐Gαolf was much greater than with β2AR‐GsαS. The difference in maximum AC activity can be explained by more rapid deactivation of Gαolf‐GTP by GTP hydrolysis and GTP dissociation relative to GsαS‐GTP. Taken together, there are biochemical differences between Gαolf and GsαS, supporting different roles of these G proteins in vivo.