Figure 2.

(Original by authors of the manuscript): The seven transmembrane alpha-helices are bound to G-protein subunits (19). These consist of alpha subunit and beta-gamma subunit complexes bound to GDP. In the inactive state, the α-subunit is bound to GDP. Upon binding of GLP-1, GDP is replaced by GTP, which then activates the α-subunit. The α-subunit and GTP complex activate signaling cascades through adenylyl cyclase and phospholipase C (20).The third intracellular loop is most important in receptor signaling.