Jj. Buggy et al., GLUCAGON-CENTER-DOT-GLUCAGON-LIKE PEPTIDE-I RECEPTOR CHIMERAS REVEAL DOMAINS THAT DETERMINE SPECIFICITY OF GLUCAGON BINDING, The Journal of biological chemistry, 270(13), 1995, pp. 7474-7478
The binding of glucagon to its hepatic receptor triggers a G-protein-m
ediated signal that ultimately leads to an increase in hepatic glucose
production (gluconeogenesis) and glycogen breakdown (glycogenolysis).
In order to elucidate the structural domain(s) of the human glucagon
receptor (hGR) involved in the selective binding of glucagon, a series
of chimeras was constructed in which various domains of the hGR were
replaced by homologous regions from the receptor for the glucoin-creti
n hormone, glucagon-like peptide I (GLP-IR), hGR and GLP-IR are quite
similar (47% amino acid identity) yet have readily distinguishable lig
and binding characteristics; glucagon binds to the recombinant hGR exp
ressed in COS-7 cells with a K-d that is 1000-fold lower than the K-d
for glucagon binding to GLP-IR, In the present study, chimeric recepto
rs were transiently expressed in COS-7 cells and analyzed for glucagon
binding, Expression of each receptor chimera was confirmed by immunof
luorescence staining using a hGR-specific monoclonal antibody, This re
port identifies several noncontiguous domains of the hGR that are impo
rtant for high affinity glucagon binding, Mast notable are the membran
e-proximal half of the amino-terminal extension, the first extracellul
ar loop, and the third, fourth, and sixth transmembrane domains.