GIPR

GIPR is the class B GPCR for glucose-dependent insulinotropic polypeptide (GIP) - the incretin hormone released by duodenal K cells after meals to potentiate glucose-stimulated insulin secretion. GIPR co-activation with GLP-1R is the pharmacological foundation of tirzepatide (Mounjaro/Zepbound), the most effective approved weight loss and diabetes drug to date. GIPR's anabolic and bone-protective effects, central satiety signals, and cardioprotective functions make it far more than just a beta-cell amplifier. Every scaffold targeting incretin biology, obesity, or cardiometabolic disease that moves beyond pure GLP-1R agonism routes through this card.

Receptor structure and signaling

GIPR (chromosome 19q13.32, 14 exons, 466 aa, ~53 kDa) adopts the canonical class B GPCR architecture: N-terminal extracellular domain (ECD) with three conserved disulfide bonds (Cys46–Cys70, Cys61–Cys103, Cys84–Cys118), seven TM helices, and a C-terminal tail with GRK phosphorylation sites for β-arrestin recruitment. GIP (42 aa, secreted from preproGIP by K cells) binds GIPR with Kd ~2 nM / Ki ~0.8 nM; it is degraded within 2–7 minutes by DPP-4 (cleavage at position 2 Ala). The two-domain binding mechanism of class B GPCRs applies: C-terminal GIP helix engages ECD, N-terminus drives TM activation. Primary signaling: Gs → adenylyl cyclase → cAMP → PKA → CREB → insulin secretion in beta cells, anabolic gene programs in adipose and bone. EPAC and Gβγ contribute parallel signals. β-Arrestin2 drives desensitization and clathrin-mediated internalization. GIPR is highly expressed in beta cells, adipose, adrenal cortex, heart, pituitary, and hippocampus. The rs10423928 A allele impairs insulin secretion and is associated with T2D risk.

Approved drugs and research recipes

Tirzepatide (GIP/GLP-1R dual agonist, 39-aa lipidated peptide) is FDA-approved for T2D and obesity - it outperforms pure GLP-1R agonists on HbA1c reduction and weight loss, in large part through GIPR co-activation. DPP-4 inhibitors (sitagliptin, saxagliptin) indirectly boost GIPR signaling by prolonging endogenous GIP. (Pro³)GIP is the canonical research GIPR antagonist (competitive, Ki ~13 nM in rodents; partial/full agonist at human receptor - a species difference that complicates antagonist translation). For peptide research, the tractable recipes are: tirzepatide-derived single-chain dual agonists with tunable GIPR/GLP-1R selectivity ratios via N-terminal substitutions; DPP-4-resistant GIP analogs (Aib substitution at position 2) for longer-acting monotherapy; GIPR-selective agonists that preserve the anabolic bone effects without full GLP-1R-mediated appetite suppression; and triagonist scaffolds (GIP/GLP-1/glucagon) using tirzepatide as the template for maximum metabolic flexibility.