Both of these analogs solve the same problem, and they solve it the same way: by making the molecule bind its carrier proteins worse. That sounds backwards until you see why those carrier proteins were the obstacle in the first place.
Native IGF-1 spends most of its time in plasma locked to IGF-binding proteins, the IGFBPs, which hold it away from its receptor. Think of the IGFBPs as the brake, and the whole design story of both analogs is about releasing it. IGF-1 LR3 and IGF-1 DES are two different ways of cutting that brake line. Here is how each one does it, and the one caveat that trips up a lot of experiments.
IGF-1 DES: snip off three residues
DES is the simpler edit. Full name des(1-3)IGF-1, which is just IGF-1 with its first three amino acids, the tripeptide Gly-Pro-Glu, removed from the N-terminus.
This isn’t a lab-only invention. The truncated form has been isolated from bovine colostrum, human brain and porcine uterus, probably from natural post-translational cleavage [1]. Francis’s group first purified it from bovine colostrum in 1988 and found it was roughly ten times more potent than intact IGF-1 at stimulating protein synthesis and DNA synthesis in rat myoblast cultures [2].
Why ten times? Because of what the missing tripeptide costs. The glutamate at position 3 is critical for IGFBP binding. Remove it and the molecule binds those carrier proteins far more weakly, which leaves more of it free to reach the receptor [1]. The receptor affinity itself barely moves. The whole gain comes from slipping the brake. That is a useful thing to know going in, because it tells you the analog is not a stronger key, it is a key that spends less time locked in a drawer.
IGF-1 LR3: add a tail, swap one residue
LR3 reaches the same destination by another road, and it combines two changes.
The “R3” part replaces the glutamate at position 3 with arginine. Same position DES deletes, different fix: instead of removing the IGFBP-binding residue, LR3 substitutes it [3]. The “L” part is a 13-amino-acid N-terminal extension, giving the “Long” in the name. Francis’s 1992 work built these as fusion peptides and showed the extension also helps the molecule fold correctly during production [3].
The result ranks like this. In cell lines that secrete IGFBPs into the medium, the order of potency ran Long [Arg3]-IGF-1 and des(1-3)IGF-1 at the top, then Long [Gly3]-IGF-1, then Long IGF-1, then native IGF-1 [3]. So DES and LR3 end up in roughly the same tier, both well ahead of the unmodified hormone, because both dodge the IGFBPs.
The caveat that ruins experiments
Here is the part most comparison pages leave out, and it matters more than the structural trivia.
The potency advantage of these analogs depends heavily on the species of your assay system. Lord’s 1994 study compared IGF-1, des(1-3)IGF-1 and LR3-IGF-1 across rat, sheep, human, pig and chicken plasma. The variants that bound extremely weakly in rat plasma bound significantly in plasma from the other species [4].
Read that again. An analog engineered to escape binding proteins in a rat may get re-captured in sheep or human plasma. The 1992 data makes the same point from the other direction: in chicken embryo fibroblasts, a cell line that secretes no detectable IGFBPs, Long [Arg3]-IGF-1 was actually less potent than plain IGF-1 [3]. No binding proteins to escape, no advantage.
So the “DES and LR3 are more potent” headline is only true in a system where IGFBPs are present and where they behave like the rat model everyone cites. Pick the wrong species or a binding-protein-free cell line and the ranking can flip.
Side by side
| IGF-1 DES | IGF-1 LR3 | |
|---|---|---|
| Structural change | Gly-Pro-Glu removed from N-terminus | Glu3 to Arg3, plus 13-residue N-terminal extension |
| Mechanism of extra potency | Loses the Glu3 that IGFBPs need | Same position altered, not deleted |
| Occurs naturally? | Yes, isolated from colostrum, brain, uterus [1] | No, engineered |
| Relative potency (IGFBP-secreting cells) | Top tier with LR3 [3] | Top tier with DES [3] |
| Potency when no IGFBPs present | Advantage disappears [3] | Can fall below native IGF-1 [3] |
Designing the comparison
Three things to lock down before you run it. Match your assay species to your question, because the rat-based potency numbers do not transfer cleanly to sheep, human, pig or chicken systems [4]. Check whether your cell line actually secretes IGFBPs, since the whole advantage of both analogs is conditional on their presence [3]. And confirm identity, because a truncation of three residues or a 13-residue extension is exactly the kind of difference a certificate of analysis should pin down by mass.
For the structural deep dive on the truncated form, see our IGF-1 DES receptor binding guide, and our IGF signaling and glucose metabolism overview covers the wider pathway.
References
- Ballard FJ, et al. Int J Biochem Cell Biol. 1996;28(10):1085-1087. PubMed 8930132
- Francis GL, et al. Biochem J. 1988;251(1):95-103. PubMed 3390164
- Francis GL, et al. J Mol Endocrinol. 1992;8(3):213-223. PubMed 1378742
- Lord AP, et al. J Endocrinol. 1994;140(3):475-482. PubMed 7514204
Disclaimer: This content is intended for research purposes only and is not meant to constitute medical advice.
This educational material discusses laboratory research concepts only. Loti Labs products are intended strictly for research and development use and are not for human consumption.
