9.A.14.4.13
Glucagon receptor of 477 aas and 7 TMSs (Family B GPCR; Hilger et al. 2020) (MacNeil et al. 1994).  It is the G-protein coupled receptor for glucagon that plays a central role in the regulation of blood glucose levels and glucose homeostasis (Zhou et al. 2009). It does so by regulating the rate of hepatic glucose production by promoting glycogen hydrolysis and gluconeogenesis, and it mediates the responses to fasting. Ligand binding causes a conformation change that triggers signaling via guanine nucleotide-binding proteins (G proteins) and modulates the activity of down-stream effectors, such as adenylate cyclase. Promotes activation of adenylate cyclase and plays a role in signaling via a phosphatidylinositol-calcium second messenger system. The 3-D structure has been determined (Siu et al. 2013; Zhang et al. 2017).  In addition, its structure with glucagon and two distinct classes of heterotrimeric G-proteins, G_s and G_i1, has been determined (Qiao et al. 2020; Chang et al. 2020).