Lipidation: fatty-acid chains on peptides, with semaglutide as a structural example
Last reviewed 2026-10-10 · Sable Peptides · Research use only
Sable research method explainer. Updated 2026-10-10. Research use only.
Short answer
Lipidation (also called acylation) attaches a fatty-acid chain to a peptide, usually through a lysine side chain or the N-terminus and often via a short hydrophilic linker. The fatty chain lets the peptide associate reversibly with hydrophobic sites, in particular on serum albumin, and with membranes. This page describes lipidation purely as a structural feature. It describes identity and structure only.
Anatomy of a lipidated peptide
A lipidated peptide has three parts: the peptide backbone, a linker and the lipid.
Semaglutide is a well-documented example. Its backbone is a GLP-1(7-37) analogue with an Aib (2-aminoisobutyric acid) substitution at position 8. Lysine 26 carries a side chain made of two 8-amino-3,6-dioxaoctanoic acid units (often abbreviated OEG or AEEA), a γ-glutamic acid spacer, and an 18-carbon fatty diacid. Lau and colleagues describe how the length of the diacid and the linker were chosen to tune albumin binding (Lau et al., 2015). Knudsen and Lau review the structural lineage from earlier analogues (Knudsen and Lau, 2019).
Tirzepatide follows the same design logic on a different 39-residue backbone, with a C20 fatty diacid attached through a γGlu-(AEEA)2 linker to a lysine side chain. Retatrutide also carries a C20 diacid on Lys17 through a γGlu/AEEA linker.
Palmitoyl peptides: a simpler form
Not all lipidation uses a diacid and linker. Matrixyl (Pal-KTTKS) and Pal-GHK carry a palmitoyl (C16) chain coupled directly to the N-terminal amine. These are compact lipopeptides, and their /ref pages give the PubChem formula and weight.
Structural consequences
Mass. The side chain adds substantial mass. Semaglutide's PubChem formula is C187H291N45O59 and its molecular weight is 4114 g/mol.
Hydrophobicity. Lipidated peptides elute later on reversed-phase HPLC and can be less soluble in purely aqueous buffers. They may also self-associate.
Analytical identity. A mass check must match the complete lipidated structure. A missing linker unit or a different fatty-acid length gives a clearly different mass, which is one of the identity checks a certificate of analysis reports.
How it is made
The backbone is usually assembled by solid-phase synthesis. The lysine to be acylated carries an orthogonal protecting group, which is removed selectively so the linker units and fatty diacid can be coupled step by step on the resin before final cleavage. Alternatively, the side chain can be attached in solution.
At Sable
Semaglutide, tirzepatide and retatrutide are listed with sourced identity data only: CAS, formula, molecular weight and sequence where on file. Sable makes no other claims about them. Batch certificates are available for every lot at /coa. Sable Peptides has been operating since 2019 and supplies every compound mentioned here as laboratory research material only. Nothing on this page is advice on use in people or animals, and no administration or medical-use information is provided.
Key terms
- Acylation
- Attaching an acyl group, here a fatty acid or fatty diacid, usually through an amide bond.
- Fatty diacid
- A long hydrocarbon chain with a carboxylic acid at each end. One end couples to the linker; the other stays free.
- OEG / AEEA
- 8-amino-3,6-dioxaoctanoic acid, a short hydrophilic spacer unit used in linkers.
- γ-Glu spacer
- A glutamic acid residue linked through its side-chain (gamma) carboxyl.
- Orthogonal protection
- Protecting groups that can be removed selectively without disturbing the others.
Common questions
What is the side chain on semaglutide?
An 18-carbon fatty diacid attached to lysine 26 through a γ-glutamic acid spacer and two OEG (AEEA) units.
Is a palmitoyl peptide lipidated?
Yes. Pal-KTTKS (Matrixyl) and Pal-GHK carry a C16 palmitoyl chain on the N-terminus.
Does Sable give any information beyond structure for these compounds?
No. Only identity and structure data are given, for research use only.
Related explainers
- PEGylation explained: attaching polyethylene glycol to a peptide
- Non-natural amino acids in peptide analogues: Aib, Nle, Dmt and others
Related reference pages
Sources
- Lau J, et al. Discovery of the once-weekly glucagon-like peptide-1 (GLP-1) analogue semaglutide. J Med Chem. 2015;58(18):7370-7380. https://doi.org/10.1021/acs.jmedchem.5b00726
- Knudsen LB, Lau J. The discovery and development of liraglutide and semaglutide. Front Endocrinol. 2019;10:155. https://doi.org/10.3389/fendo.2019.00155
- Karle IL, Balaram P. Structural characteristics of alpha-helical peptide molecules containing Aib residues. Biochemistry. 1990;29(29):6747-6756. https://doi.org/10.1021/bi00481a001
Questions
What is the side chain on semaglutide?
An 18-carbon fatty diacid attached to lysine 26 through a γ-glutamic acid spacer and two OEG (AEEA) units.
Is a palmitoyl peptide lipidated?
Yes. Pal-KTTKS (Matrixyl) and Pal-GHK carry a C16 palmitoyl chain on the N-terminus.
Does Sable give any information beyond structure for these compounds?
No. Only identity and structure data are given, for research use only.
Sources
CoA for every lot — request yours and we email it within 2 hours.
Research use only. Not for human or veterinary use. No health claims.