BULKGLP RESEARCH LIBRARY
GLP-1, GIP, and Glucagon Receptor Mechanics
Published
Semaglutide targets GLP-1R, Tirzepatide targets GLP-1R and GIPR, and Retatrutide targets GLP-1R, GIPR and the glucagon receptor, GCGR.
At a glance
- Single, dual and triple agonism describe the receptor targets a molecule activates.
- Sequence substitutions and fatty diacid side chains serve different structural functions.
- Binding affinity and signaling potency are different measurements; assay conditions matter.
Compare receptor targets
| Analogue | Targets | Structural reference |
|---|---|---|
| Semaglutide | GLP-1R | GLP-1 analogue with an Aib substitution and C18 fatty diacid side chain |
| Tirzepatide | GLP-1R and GIPR | 39-residue GIP-derived peptide with a C20 fatty diacid side chain |
| Retatrutide | GLP-1R, GIPR and GCGR | 39-residue GIP-derived peptide with a C20 fatty diacid side chain |
These receptors are G protein-coupled receptors. In cell-based experiments, activation can be measured through cyclic AMP, abbreviated cAMP, an intracellular signaling molecule. The target list identifies the scope of activity; it does not imply equal activity at every receptor or identical behavior in every assay.
What the chemical modifications do
Aib means alpha-aminoisobutyric acid, a nonstandard amino acid used in these peptide designs. Substitution near the peptide's amino terminus can reduce cleavage by dipeptidyl peptidase-4, or DPP-4. Retatrutide and Tirzepatide include Aib at position 2; Semaglutide includes the corresponding substitution at GLP-1 position 8.
Fatty diacid attachment, called acylation, promotes albumin binding. Semaglutide is modified at Lys26, Tirzepatide at Lys20 and Retatrutide at Lys17 through their respective linkers. Albumin in the assay medium can change the freely available compound and shift measured responses. Do not attribute resistance to DPP-4 solely to the fatty side chain.
Read affinity and potency correctly
- Binding affinity: Kd or Ki
- Describes receptor binding under the specified method. A lower value generally indicates stronger binding within a comparable experiment.
- Functional potency: EC50
- The concentration producing half the measured response range in a defined signaling assay. It is not a direct measurement of binding affinity.
- Maximum response: Emax
- The largest response measured in that assay, relative to the specified reference and normalization.
The original Retatrutide paper reports cAMP EC50 values of 0.0643 nM at GIPR, 0.775 nM at GLP-1R and 5.79 nM at GCGR in its recombinant receptor cell assays. These are functional potency results for that experimental system. They cannot be combined with binding values from another paper to create a reliable ranking of the three compounds.
Set up a useful comparison
Use the same receptor construct, cell system, receptor expression, incubation time, albumin conditions and reference agonist. Record the pathway measured and the complete concentration-response curve. Distinguish an intact-mass identity result from evidence of receptor activity.
For material selection, review the lot records for Semaglutide, Tirzepatide and Retatrutide. Use the COA guide to separate identity, purity and measured content.