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J. Biol. Chem., Vol. 278, Issue 12, 10195-10200, March 21, 2003
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From the Two fragments of the receptor for
glucagon-like peptide-1 (GLP-1), each containing the N-terminal domain,
were expressed and characterized in either bacterial or mammalian
cells. The first fragment, rNT-TM1, included the N-terminal domain and
first transmembrane helix and was stably expressed in the membrane of
human embryonic kidney 293 cells. The second, 6H-rNT, consisted of only
the N-terminal domain of the receptor fused with a polyhistidine tag at
its N terminus. The latter fragment was expressed in Escherichia
coli in the form of inclusion bodies from which the protein was
subsequently purified and refolded in vitro. Although both
receptor fragments displayed negligible 125I-labeled
GLP-1(7-36)amide-specific binding, they both displayed high affinity
for the radiolabeled peptide antagonist
125I-exendin-4(9-39). Competition binding studies
demonstrated that the N-terminal domain of the GLP-1 receptor maintains
high affinity for the agonist exendin-4 as well as the antagonists
exendin-4(3-39) and exendin-4(9-39) whereas, in contrast, GLP-1
affinity was greatly reduced. This study shows that although the
exendin antagonists are not dependent upon the extracellular loops and
transmembrane helices for maintaining their normal high affinity
binding, the endogenous agonist GLP-1 requires regions outside of the
N-terminal domain. Hence, distinct structural features in exendin-4,
between residues 9 and 39, provide additional affinity for the
N-terminal domain of the receptor. These data are consistent with a
model for the binding of peptide ligands to the GLP-1 receptor in which the central and C-terminal regions of the peptides bind to the N
terminus of the receptor, whereas the N-terminal residues of peptide
agonists interact with the extracellular loops and transmembrane helices.
The Isolated N-terminal Domain of the Glucagon-like Peptide-1
(GLP-1) Receptor Binds Exendin Peptides with Much Higher Affinity than
GLP-1*
,
,
¶
School of Biomedical Sciences, University of
Leeds, Leeds, LS2 9JT, United Kingdom and the
§ Institut für Biotechnologie der
Martin-Luther-Universität Halle-Wittenberg, Kurt-Mothes-Strasse
3, D-06120 Halle, Germany
*
This work was supported by the Basque government and
Diabetes UK.The costs of publication of this
article were defrayed in part by the
payment of page charges. The article
must therefore be hereby marked
"advertisement" in
accordance with 18 U.S.C. Section
1734 solely to indicate this fact.
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