-
Views
-
Cite
Cite
Richard W. Gelling, Michael B. Wheeler, Jiaping Xue, Sandor Gyomorey, Cuilan Nian, Raymond A. Pederson, Christopher H. S. McIntosh, Localization of the Domains Involved in Ligand Binding and Activation of the Glucose-Dependent Insulinotropic Polypeptide Receptor, Endocrinology, Volume 138, Issue 6, June 1997, Pages 2640–2643, https://doi.org/10.1210/endo.138.6.9104
- Share Icon Share
Abstract
The receptors for the two structurally related insulinotropic hormones Glucose-dependent Insulinotropic Polypeptide (GIP) and Glucagon-Like Peptide-1 (GLP-1) share approximately 40% sequence identity and demonstrate complete specificity for their endogenous ligands, while utilizing similar second messsenger pathways. In the current study chimeric GIP-GLP-1 receptors were prepared, and the effect of domain-exchange on ligand binding and adenylyl cyclase activation examined. A chimera (CH-2) consisting of the first 132 amino acids of the external N-terminal (NT) domain bound 125I-GIP with high affinity (27.77 ± 11.85 nM). However, for receptor coupling to cAMP production it was necessary to extend the NT into the first transmembrane (TM-1) region (CH-3: IC50 = 9.04 ± 1.07 nM; EC50 = 17.1 ± 3.5 nM). A chimera which included part of TM-3 (CH-4) demonstrated binding and signalling (IC50 = 8.33 ± 0.14 nM; EC50 = 467.5 ± 173.6 pM) similar to the wild type receptor (IC50 = 1.33 ± 0.19 nM; EC50 = 497.9 ± 211.7 pM). Surprisingly constructs CH-2 and CH-3, while devoid of detectable 125I-GLP-1 binding, were capable of eliciting GLP-1-specific cAMP production (EC50s CH-2 = 81.4 ± 19.6 nM; CH-3 = 5.99 ± 0.68 nM) suggesting that receptor activation is not completely dependent on high affinity receptor binding. These data clearly demonstrate that the NT domain of the GIP receptor acts as the ligand-specific binding domain and that the first transmembrane domain is important for receptor activation.