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Updated: Jun 26, 2026

Measuring G-protein-coupled Receptor Signaling via Radio-labeled GTP Binding
Published on: June 9, 2017
Structural insight into G-protein coupled receptor binding by apelin.
David N Langelaan1, E Meghan Bebbington, Tyler Reddy
1Department of Biochemistry & Molecular Biology, Dalhousie University, Halifax, Nova Scotia B3H 1X5 Canada.
Apelin peptides, ligands for APJ receptors, show increased structure at low temperatures. This structural change, particularly in key binding regions, suggests a temperature-dependent mechanism for apelin-APJ receptor interaction.
Area of Science:
- Biochemistry
- Structural Biology
- Molecular Biology
Background:
- Apelin peptides are endogenous ligands for the G-protein coupled receptor APJ.
- Apelin plays roles in cardiovascular and central nervous systems, glucose metabolism, and as an HIV-1 coreceptor.
- Apelin exists in various isoforms (13-36 residues) in vivo.
Purpose of the Study:
- To compare the structures of five apelin isoforms at physiological (35°C) and low (5-6°C) temperatures.
- To elucidate the structural basis for apelin-APJ receptor interactions.
Main Methods:
- Circular Dichroism (CD) spectroscopy
- Nuclear Magnetic Resonance (NMR) spectroscopy
- Site-directed mutagenesis (F13A-apelin-13)
Main Results:
- Apelin isoforms exhibit increased structural content at low temperatures compared to physiological temperatures.
- Specific regions (R6-L9 and G13-F17) of apelin-17 become highly structured at 5°C, correlating with CD spectral properties.
- Cis-trans peptide bond isomerization at P14 and P16 was observed, leading to distinct conformers.
- Apelin-12, apelin-13, and pyroglutamate-apelin-13 show similar structures and isomerization patterns.
Conclusions:
- Temperature significantly influences apelin peptide structure, impacting functionally critical regions.
- The observed structural changes and isomerization suggest a potential two-step mechanism for apelin-APJ binding and activation.
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