Minimal binding to other class B1 GPCRs for [125I]-hGLP-2(1-33,M10Y) and [125I]-hGLP-2(3-33,M10Y)
Given the high sequence similarity between class B1 receptors and their peptide ligands, we next determined whether the two radioligands cross-react with the closely related class B1 GPCRs; hGIPR, hGLP-1R, hGCGR and hSecretinR, VPAC-1R, and VPAC-2R (figure 4a). While we observed no specific binding for five of the six receptors, a low, but significant binding was observed for both radioligands to the hGLP-1R (Emax of 37.8% and 26.7% of the hGLP-2R binding) (figure 4b and supplementary figure 1).
Furthermore, we tested the binding properties of both radioligands on the mouse and rat GLP. Also here, we observed high-affinity binding (figure 5a,b and table 2). The similar IC50 values of hGLP-2(1-33) on the GLP-2R from the three species suggests overall strong structural similarities between the receptors (table 2).