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IGF-1 LR3: A Research Overview of the Long R3 IGF-I Analog

By The Bionova Club Team

Research use only. Bionova products are sold strictly for in-vitro and laboratory research by qualified professionals. They are not drugs, food, or cosmetics, are not approved by the FDA, and are not for human or veterinary use. Nothing in this article is medical advice or a claim about effects in people.

Disclosure: Bionova Club sells IGF-1 LR3 in a 1 mg vial, linked below.

IGF-1 LR3, also written Long R3 IGF-I or LR3 IGF-1, is an engineered version of insulin-like growth factor I (IGF-I). It was designed in the early 1990s as a laboratory tool, and its two changes, one longer end and one swapped amino acid, were chosen to answer a specific research question: how much of IGF-I's activity in cell culture is controlled by the binding proteins that hold onto it?

This overview covers the parent molecule, the history of its discovery, the receptor and binding-protein system it belongs to, how the LR3 analog was built, which models have studied it, and how the dry material is checked and stored. It covers chemistry and research history only.

What is IGF-I, the parent molecule?

Human IGF-I is a single polypeptide chain of 70 amino acids cross-linked by three disulfide bridges, with a calculated molecular weight of 7,649. Its sequence was published in 1978 by Rinderknecht and Humbel, who noted its clear structural similarity to proinsulin (Rinderknecht & Humbel, 1978, Journal of Biological Chemistry). The name "insulin-like" is older than the full sequence: it goes back to the serum activity called nonsuppressible insulin-like activity (NSILA), and the 1976 naming paper tied it to structural homology with insulin (Rinderknecht & Humbel, 1976).

At 70 residues, IGF-I sits on the protein side of the usual peptide-versus-protein line. Our primer What are peptides? explains where that line is usually drawn.

A short history

The research trail starts in 1957, when William Salmon and William Daughaday described a serum factor, controlled by pituitary hormones, that stimulated sulfate incorporation into cartilage in vitro (Salmon & Daughaday, 1957, Journal of Laboratory and Clinical Medicine). The activity was first called "sulfation factor." Over the following two decades the responsible molecules were purified and sequenced, and in 1976 Rinderknecht and Humbel proposed the name insulin-like growth factor (IGF), based on amino-terminal sequence homology with the insulin B chain (Rinderknecht & Humbel, 1976, PNAS).

The IGF system: receptor and binding proteins

Two kinds of partner molecule shape how IGF-I behaves in an experiment.

  • The type 1 IGF receptor (IGF-1R). This cell-surface receptor is closely related to the insulin receptor. Its complete primary structure was determined from cloned cDNA in 1986. It is made as a single precursor that is cut into alpha and beta subunits, in the same arrangement as the insulin receptor (Ullrich et al., 1986, EMBO Journal). It belongs to the receptor tyrosine kinase class.
  • IGF-binding proteins (IGFBPs). A family of six binding proteins attaches to IGFs in serum and in culture medium, and binding to them affects how much IGF is free to reach the receptor (Jones & Clemmons, 1995, Endocrine Reviews).

Because many cultured cells secrete their own IGFBPs, the measured activity of IGF-I in a dish depends partly on those binding proteins and not only on the receptor. The LR3 analog was built to separate those two influences.

From des(1-3)IGF-I to Long R3 IGF-I

The truncated form

In the late 1980s, researchers in Adelaide isolated a naturally occurring truncated IGF-I from bovine colostrum that lacked the first three residues (Gly-Pro-Glu) (Francis et al., 1988, Biochemical Journal). This form, des(1-3)IGF-I, has much weaker binding to IGFBPs. A later review attributed that change to the missing glutamate at position 3 (Ballard et al., 1996, International Journal of Biochemistry & Cell Biology).

The LR3 design

In 1992 the same research group described a set of IGF-I fusion analogs expressed in Escherichia coli (Francis et al., 1992, Journal of Molecular Endocrinology). One of them, Long [Arg3]-IGF-I, is the molecule now sold as IGF-1 LR3. It differs from human IGF-I in two ways:

  1. "Long": a 13-residue N-terminal extension, made of the first 11 amino acids of methionyl porcine growth hormone followed by Val-Asn.
  2. "R3": arginine in place of glutamic acid at position 3 of the IGF-I sequence. This is the same position whose loss in des(1-3)IGF-I weakens IGFBP binding.

The authors reported that the hydrophobic extension appeared to help the protein fold correctly during production, giving high yields of active product (Francis et al., 1992).

  • Length
    • Human IGF-I: 70 residues
    • IGF-1 LR3 (Long R3 IGF-I): 83 residues
  • N-terminus
    • Human IGF-I: Gly-Pro-Glu…
    • IGF-1 LR3 (Long R3 IGF-I): 13-residue extension, then Gly-Pro-Arg…
  • Position 3 (IGF-I numbering)
    • Human IGF-I: Glu
    • IGF-1 LR3 (Long R3 IGF-I): Arg
  • Disulfide bridges
    • Human IGF-I: 3
    • IGF-1 LR3 (Long R3 IGF-I): 3 (same IGF-I core)
  • Molecular weight
    • Human IGF-I: ~7.65 kDa
    • IGF-1 LR3 (Long R3 IGF-I): ~9.1 kDa (calculated from sequence)
  • Typical production
    • Human IGF-I: Recombinant
    • IGF-1 LR3 (Long R3 IGF-I): Recombinant (E. coli)
  • Bionova format

Bionova's product page lists the molecular formula as C₄₀₀H₆₂₅N₁₁₁O₁₁₅S₉. Forming the three disulfide bridges removes six hydrogen atoms from that count.

What has been studied, and in which models

The original characterization was done in cultured cells. Francis and colleagues compared the analogs with authentic IGF-I and des(1-3)IGF-I in several cell lines, measuring protein and DNA synthesis (Francis et al., 1992). Two findings define the analog's use as a tool:

  • In cell lines that secrete IGFBPs into the medium, Long [Arg3]-IGF-I and des(1-3)IGF-I were the most potent of the molecules compared.
  • In chicken embryo fibroblasts, which do not secrete detectable IGFBPs, Long [Arg3]-IGF-I was less potent than IGF-I.

The authors read this as evidence that the analog's higher potency in culture comes mainly from reduced IGFBP interaction, not from stronger receptor binding. That is the reason later in-vitro studies use it: as an IGF-I analog with low affinity for binding proteins. For example, it has been used alongside recombinant IGF-I in serum-free culture of bovine ovarian follicles to study how IGF bioavailability is regulated in that system (Thomas et al., 2007, Reproduction).

These are results from specific cell and tissue-culture models. They are not evidence of any effect in people, and IGF-1 LR3 is not approved by the FDA as a drug.

For other research peptides studied in connection with growth-hormone release, compared by structure and receptor class, see CJC-1295, ipamorelin and tesamorelin and ipamorelin vs GHRP-2 vs GHRP-6.

Analytical and quality checks

IGF-1 LR3 is a recombinant protein, so its quality checks look more like those for a small protein than for a short synthetic peptide.

  • Identity by mass spectrometry. An intact mass near 9.1 kDa is consistent with the 83-residue sequence. A mass near 7.65 kDa would suggest native IGF-I instead.
  • Purity by reversed-phase HPLC. This is the standard purity measure reported for research peptides and small proteins.
  • Correct folding. IGF-I has three disulfide bridges, and the 1992 paper treats correct folding as a key step in producing active material (Francis et al., 1992). Misfolded variants can have the same mass but elute differently on HPLC.
  • Name check. "IGF-1," "IGF-1 LR3," "des(1-3)IGF-I" and "IGF-1 DES" are different molecules. Check the sequence and mass on the documentation, not just the name.

Storage notes for lyophilized IGF-1 LR3

  • Keep it sealed, cold and dry. Store the lyophilized powder in its original sealed vial, away from light and moisture.
  • Warm before opening. Let a sealed vial reach room temperature before opening so moisture does not condense on the powder.
  • Check the appearance. Bionova IGF-1 LR3 is supplied as a white lyophilized powder. Material that looks wet, clumped or discolored should be reported to the supplier.
  • Follow the label. Store as directed on the product label and batch documentation.

This guide covers only the sealed, dry material. It does not cover preparing solutions.

Key takeaways

  • IGF-1 LR3 (Long R3 IGF-I) is an 83-residue recombinant analog of 70-residue human IGF-I.
  • It adds a 13-residue N-terminal extension and replaces Glu3 with Arg.
  • IGF-I acts through the type 1 IGF receptor, a receptor tyrosine kinase related to the insulin receptor, and is bound by six IGF-binding proteins.
  • The 1992 cell-culture work linked the analog's higher potency in culture to reduced IGFBP binding, not to stronger receptor binding.
  • Identity is checked by intact mass (~9.1 kDa) and purity by HPLC. Keep the dry material sealed, cold and dry.
  • Bionova sells IGF-1 LR3 in a 1 mg vial. It is a research material only and is not approved for human use.

Frequently asked questions

What does LR3 stand for?

"Long" refers to the 13-amino-acid N-terminal extension, and "R3" refers to arginine (R) replacing glutamic acid at position 3 of the IGF-I sequence.

How is IGF-1 LR3 different from IGF-1?

IGF-1 LR3 is 83 residues long instead of 70, has an arginine at IGF-I position 3, and binds IGF-binding proteins much more weakly in cell-culture studies.

Who developed IGF-1 LR3?

It was described in 1992 by Francis and colleagues in Adelaide, Australia, as one of a set of recombinant IGF-I fusion analogs made in E. coli.

What is des(1-3)IGF-I?

A naturally occurring truncated form of IGF-I that lacks the first three residues, Gly-Pro-Glu. It was isolated from bovine colostrum and also binds IGF-binding proteins weakly.

What receptor does IGF-1 LR3 act on?

In cell-culture research it acts through the type 1 IGF receptor, a receptor tyrosine kinase closely related to the insulin receptor.

How should lyophilized IGF-1 LR3 be stored?

Keep the sealed vial cold, dry and away from light, let it reach room temperature before opening, and store it as directed on the product label.

Shop for your research: IGF-1 LR3 for laboratory research. Use code CLUB10 at checkout for 10% off.

References

  1. Salmon WD Jr, Daughaday WH. A hormonally controlled serum factor which stimulates sulfate incorporation by cartilage in vitro. J Lab Clin Med. 1957. https://pubmed.ncbi.nlm.nih.gov/13429201/
  2. Rinderknecht E, Humbel RE. The amino acid sequence of human insulin-like growth factor I and its structural homology with proinsulin. J Biol Chem. 1978. https://pubmed.ncbi.nlm.nih.gov/632300/
  3. Ullrich A, et al. Insulin-like growth factor I receptor primary structure: comparison with insulin receptor suggests structural determinants that define functional specificity. EMBO J. 1986. https://pubmed.ncbi.nlm.nih.gov/2877871/
  4. Jones JI, Clemmons DR. Insulin-like growth factors and their binding proteins: biological actions. Endocr Rev. 1995. https://pubmed.ncbi.nlm.nih.gov/7758431/
  5. Francis GL, et al. Insulin-like growth factors 1 and 2 in bovine colostrum. Sequences and biological activities compared with those of a potent truncated form. Biochem J. 1988. https://pubmed.ncbi.nlm.nih.gov/3390164/
  6. Ballard FJ, Wallace JC, Francis GL, Read LC, Tomas FM. Des(1-3)IGF-I: a truncated form of insulin-like growth factor-I. Int J Biochem Cell Biol. 1996. https://pubmed.ncbi.nlm.nih.gov/8930132/
  7. Francis GL, et al. Novel recombinant fusion protein analogues of insulin-like growth factor (IGF)-I indicate the relative importance of IGF-binding protein and receptor binding for enhanced biological potency. J Mol Endocrinol. 1992. https://pubmed.ncbi.nlm.nih.gov/1378742/
  8. Thomas FH, et al. Effects of IGF-I bioavailability on bovine preantral follicular development in vitro. Reproduction. 2007. https://pubmed.ncbi.nlm.nih.gov/17636166/
  9. Rinderknecht E, Humbel RE. Amino-terminal sequences of two polypeptides from human serum with nonsuppressible insulin-like and cell-growth-promoting activities: evidence for structural homology with insulin B chain. Proc Natl Acad Sci U S A. 1976. https://pubmed.ncbi.nlm.nih.gov/1069990/

For laboratory research use only. Not for human consumption.