First cryo-EM structures of tirzepatide bound to both incretin receptors

Researchers led by Zhao and colleagues reported the first cryo-electron microscopy structures of tirzepatide bound to its two target receptors, publishing the work in Nature Communications on February 25, 2022.^[1] Tirzepatide, sold as Mounjaro and Zepbound, is built to activate both the GIP receptor (GIPR) and the GLP-1 receptor (GLP-1R) at once, rather than targeting only one receptor the way semaglutide (Ozempic, Wegovy, Rybelsus) does.^[1]

The team solved the structure of tirzepatide bound to the human GIPR paired with its G protein at 3.4 angstrom resolution, deposited in the Protein Data Bank as entry 7FIY, and a matching structure of tirzepatide bound to GLP-1R, deposited as entry 7FIM.^[1][2] An angstrom is a unit smaller than a nanometer, and 3.4 angstroms is fine enough to see how individual amino acids in the drug fit into pockets on the receptor surface.^[1]

Alongside the tirzepatide structures, the researchers also solved three more structures showing a related experimental peptide called peptide 20 bound to GIPR, GLP-1R, and the glucagon receptor (GCGR).^[1] Peptide 20 is a triagonist, meaning it is designed to activate all three receptors, and had completed phase 1 clinical trials at the time of the study.^[1] In total the paper reports five cryo-EM structures of these drug-receptor pairs, all captured together with their Gs signaling proteins.^[1]

The paper says tirzepatide has shown "a profound therapeutic superiority in reducing blood glucose and body weight" compared with semaglutide and dulaglutide in head-to-head clinical trials, citing earlier published trial data.^[1] The researchers write that their structural work aims to explain the molecular basis for that difference by showing exactly how the drug engages each receptor.^[1] They also note that in animal studies, activating the glucagon receptor alongside GIP and GLP-1 receptors reduced body weight, lowered fasting blood glucose, decreased HbA1c, and protected pancreatic islet tissue in a diabetic rat model, and the authors state that retaining glucagon receptor activity is what allows drugs like peptide 20 to outperform GLP-1 medicines used alone.^[1]

Why it matters for patients

This study is basic laboratory science, not a clinical trial, and it does not change how tirzepatide is prescribed or dosed. But structural biology like this helps explain, at the molecular level, why a dual-target drug such as tirzepatide can produce different effects on blood sugar and weight than a single-target drug such as semaglutide, an idea that has been discussed based on clinical trial results but had not been shown this directly at the atomic level before.^[1]

For people already taking Mounjaro or Zepbound, or considering them, the findings do not add new safety information and are not a reason to change a treatment plan. The practical value is mostly for future drug design: understanding precisely how tirzepatide grips GIPR and GLP-1R gives chemists a blueprint for designing next-generation molecules, including multi-target peptides like peptide 20, that might fine-tune effects on weight, blood sugar, or side effects.^[1]

What happens next

The paper does not describe specific new clinical trials tied to this structural data. It does note that peptide 20 had already finished phase 1 testing as of publication, and that more than a dozen other multi-target peptides aimed at GIPR, GLP-1R, or GCGR were in clinical development across the field at that time, though the sources do not give updated status on those programs.^[1] Whether these structural insights lead to new approved drugs is not yet known from the sources provided.