Research Use Only — Not for Human Consumption. All content below is intended exclusively for qualified laboratory researchers. Nothing on this page is medical advice, and no product discussed is intended for human or veterinary use.
Introduction
Retatrutide (development code LY3437943) is an investigational synthetic peptide by Eli Lilly that functions as a single-molecule agonist at three class B1 GPCRs: GIPR, GLP-1R, and GCGR. A 39-amino-acid peptide on a native GIP backbone with non-natural amino acids and a lipidated side chain. Valuable to laboratories as a benchmark for comparative multi-agonist studies and as illustration of the modern incretin-design toolkit. Strictly laboratory research; investigational compound, not an approved medicine.
Molecular Structure and Engineered Design
CAS 2381089-83-2, formula C221H342N46O68, MW ~4731.33 g/mol (PubChem CID 171390338). Features: GIP-derived backbone; Aib at positions 2 and 13 (DPP-4 resistance, helix constraint); α-methyl leucine rigidifying the mid-chain helix; lipidated lysine (C20 fatty diacid via γ-glutamate spacer and AEEA linker) driving albumin binding for once-weekly PK profile; C-terminal amidation. Reported sequence: Tyr–Aib–Gln–Gly–Thr–Phe–Thr–Ser–Asp–Tyr–Ser–Ile–α-Me-Leu–Leu–Asp–Lys(lipid)–Ala–Gln–Aib–Ala–Phe–Ile–Glu–Tyr–Leu–Leu–Glu–Gly–Gly–Pro–Ser–Ser–Gly–Ala–Pro–Pro–Pro–Ser–NH2.
In Vitro Receptor Pharmacology
Coskun et al., Cell Metabolism 2022: cAMP accumulation assays in clonal HEK-293 lines with low receptor densities. Full agonist at all three receptors: human GCGR EC50 5.79 nM (vs 1.97 nM native glucagon); human GIPR EC50 0.0643 nM (vs 0.574 nM native GIP, ~8.9-fold more potent); human GLP-1R EC50 0.775 nM (vs 0.312 nM native GLP-1). GIPR-biased balance distinguishing it from dual agonists like tirzepatide.
Radioreceptor Binding Assays and Endogenous Cell Models
binding confirmed by radioreceptor assays; differentiated human adipocytes (GIPR, lipolysis regulation) and iPSC-derived hepatocytes (GCGR, glucose output) used as endogenous models; comparator panels of mono/dual/triple agonists run in the same systems.
Structural Biology: Cryo-EM Insights
2024 Cell Discovery study resolved cryo-EM structures of retatrutide bound to GLP-1R, GIPR, and GCGR with Gs heterotrimer; interaction fingerprints for the N-terminal nine residues mapped with class B1 numbering; paired with mutagenesis and cAMP assays.
Analytical Characterization
identity by high-resolution MS (exact mass 4730.4784) plus peptide mapping for non-natural residues; RP-HPLC must resolve des-lipid species, incomplete coupling products, deletion sequences, oxidation products; salt form (acetate/TFA) documented on COA; InChIKey MLOLQJNKXBNWFW-SAGGEDDASA-N; surfactant-like aggregation checked by SEC/DLS before cell assays.
Laboratory Study Applications
multi-receptor pharmacology benchmarking; biased-signaling studies (β-arrestin vs G-protein); class B1 GPCR structural research using cryo-EM maps; analytical method development for lipidated peptides.
Literature Context
Coskun T et al., Cell Metab. 2022;34(9):1234–1247; Structural insights into triple agonism, Cell Discov. 2024;10:63; Jastreboff AM et al., N Engl J Med. 2023;389(6):514–526.
Conclusion
retatrutide is one of the most instructive molecules in contemporary peptide research; every experiment belongs in the research laboratory and every sample must be analytically verified.
Research Use Only — Not for Human Consumption. This material is for qualified laboratory researchers and describes laboratory applications only. It contains no medical, therapeutic, dosing, or reconstitution guidance, and no product described here is intended for human or veterinary use.