Selank is a synthetic tuftsin-derived heptapeptide that shows how a short natural immune fragment can be redesigned for stability in the laboratory. The parent fragment it is built on lasts only moments once enzymes reach it. That fragility is the central chemistry problem this molecule was made to solve.

The answer was a small addition to the end of the chain. Understanding that addition, and the four-residue sequence it protects, explains why Selank has become a recurring subject in published peptide research. This article stays on the molecule itself: its structure, the extension that stabilizes it, and what laboratory studies have measured about how it interacts with cells and enzymes.

At Janera Science, every compound we supply is defined first by its chemistry. Selank is a clear case study in why sequence design matters, so it is worth examining closely.

What Selank Is: A Heptapeptide Built From Tuftsin

Selank is a synthetic heptapeptide that pairs the four-residue tuftsin sequence with a short stabilizing tail. A heptapeptide is a peptide made of seven amino acids joined by peptide bonds. Selank is a synthetic analogue of the natural peptide tuftsin, developed at the Institute of Molecular Genetics of the Russian Academy of Sciences in Moscow (Wikipedia, 2026).

That origin places Selank alongside Semax, the other well-known heptapeptide to come out of the same Russian molecular-genetics research. The two share more than a birthplace, as the sections below show.

The parent molecule: tuftsin

Tuftsin is a natural tetrapeptide, a peptide of four amino acids, with the sequence Thr-Lys-Pro-Arg, abbreviated TKPR. It is not a free-standing hormone. Tuftsin is a fragment located in the Fc domain of the heavy chain of immunoglobulin G, spanning residues 289 to 292, and it takes its name from Tufts University, where it was first characterized (Wikipedia, 2026).

Selank keeps that entire four-residue tuftsin sequence at its front end, then extends it. What gets added is the key to the molecule. Reading a sequence like TKPR in three-letter and one-letter form is a small skill worth having, and our guide to peptide nomenclature walks through how these codes work.

The Selank sequence and molecular identity

The full sequence of Selank is Thr-Lys-Pro-Arg-Pro-Gly-Pro, often abbreviated TKPRPGP. The first four residues are tuftsin; the final three, Pro-Gly-Pro, are a synthetic addition.

The table below lists the molecular identity data that appears on analytical documentation for the compound.

The three proline residues in the sequence, one inside the tuftsin core and two in the added tail, give the molecule chemistry that reaches beyond its length. That proline content is where the stability story begins.

The Pro-Gly-Pro Extension: Engineering Stability Into a Fragment

The three residues at the end of Selank carry the whole design. Pro-Gly-Pro is a proline-glycine-proline tripeptide added to the C-terminus to slow enzymatic breakdown of the peptide. Removing it returns the molecule to something close to the fragile parent tetrapeptide.

Why the native tuftsin fragment degrades quickly

Small peptides are exposed. Their ends and their internal bonds are open to a wide range of enzymes called peptidases, which cleave peptide bonds and cut the chain into pieces. A free tuftsin tetrapeptide is cleared rapidly once these enzymes act on it.

For a molecule meant to survive long enough to reach and interact with a target in a research model, rapid cleavage is the limiting factor. A stabilizing strategy has to protect the vulnerable end of the chain.

How Pro-Gly-Pro resists peptidases

Proline is an unusual amino acid. Its side chain loops back and bonds to its own backbone nitrogen, forming a rigid ring that most peptidases struggle to accommodate. Placing proline at and near the C-terminus creates steric hindrance, a physical crowding that blocks the enzyme from fitting the bond it would otherwise cleave.

The effect matters because tuftsin on its own is a poor research subject once peptidases reach it. Capping the sequence with Pro-Gly-Pro converts a short-lived fragment into a defined molecule stable enough to study, without changing the tuftsin residues that give the peptide its recognition character.

A shared stabilization strategy with Semax

The same Pro-Gly-Pro tail appears on Semax, the other heptapeptide from the same Russian research programme. Semax places the extension on a fragment of adrenocorticotropic hormone; Selank places it on tuftsin. The parent sequences differ, yet the stabilization approach is identical.

This is a deliberate molecular-design pattern. Take a short natural sequence with interesting properties, then cap it with Pro-Gly-Pro so it lasts long enough to study. Reading the two molecules side by side makes the strategy easier to recognize, and the Semax chemistry article covers the ACTH side in full.

What the Extension Preserves: Tuftsin's Molecular Lineage

Adding Pro-Gly-Pro stabilizes the chain while leaving the front of the molecule intact. The Thr-Lys-Pro-Arg sequence stays at the N-terminus, so Selank carries the tuftsin recognition motif into a longer, more durable peptide.

Tuftsin itself is described in the literature as an immunomodulatory peptide, one that interacts with cells of the immune system (Wikipedia, 2026). Keeping the full tuftsin sequence is what connects Selank to that lineage at the molecular level. This is a structural point about which residues are conserved, and it explains why a share of the published research on Selank examines immune-related gene and protein activity, covered in the survey below.

Published Laboratory Research on Selank's Molecular Interactions

The literature on Selank spans enzyme inhibition, immune-gene expression, and neurotrophic-factor expression. The studies below are laboratory research in cell, serum, and animal models, reported here to describe what has been measured at the molecular level. None of it describes use in humans.

Enkephalin-degrading enzyme inhibition

One of the most-studied molecular properties of Selank is its effect on the enzymes that break down enkephalins, short signalling peptides in the body. In human serum, Selank inhibited these enkephalin-degrading enzymes with a half-maximal inhibitory concentration of about 20 micromolar, and Semax did so at about 10 micromolar, both more potent than the reference peptidase inhibitors puromycin and bacitracin (Russian Journal of Bioorganic Chemistry, 2001).

The same effect was measured in blood plasma. Selank dose-dependently inhibited the hydrolysis of plasma enkephalin with a half-maximal inhibitory concentration near 15 micromolar (Bulletin of Experimental Biology and Medicine, 2001). A half-maximal value in the low micromolar range indicates a genuine, measurable interaction with the enzyme system rather than a weak or incidental effect.

Inflammation-related gene expression

A separate line of research maps how Selank changes gene expression in immune tissue, the molecular reflection of its tuftsin lineage. In mouse spleen, a single injection of Selank significantly altered the expression of 34 of 84 inflammation-related genes measured, spanning chemokines, cytokines, and their receptors (Regulatory Peptides, 2011).

Within that response, the peptide induced expression of the interferon-alpha gene while leaving several other cytokine genes, including interleukin-4 and tumour necrosis factor-alpha, unchanged. A selective rather than blanket shift in gene expression points to a specific molecular action, which is the kind of detail that distinguishes a defined peptide from a general stimulant of the cell.

Neurotrophic-factor expression: BDNF

Other work has examined how Selank relates to brain-derived neurotrophic factor (BDNF), a protein that supports nerve cell function. In rat hippocampus, intranasal administration of Selank raised Bdnf messenger RNA levels three hours after dosing and BDNF protein levels twenty-four hours after dosing, at two separate doses (Doklady Biological Sciences, 2008).

The sequence of those measurements is itself informative. A rise in messenger RNA followed by a later rise in protein is the expected order for a change in gene expression, since the cell transcribes the gene before it translates the protein. The finding places Selank's measured activity at the level of gene and protein expression in the tissue studied.

Handling, Synthesis, and Verification Context

A molecule this defined only stays defined if it is made and checked properly. Selank is produced by solid-phase synthesis, the standard method for assembling peptides one residue at a time on a solid support, then supplied as a lyophilized, or freeze-dried, powder for stability. The lyophilized powder form keeps the peptide dry and shelf-stable until a researcher reconstitutes it.

Confirming that a vial contains the correct seven-residue sequence at high purity requires analytical testing. HPLC and mass spectrometry together verify purity and molecular identity, and the results appear on a lot-specific Certificate of Analysis. You can review those documents on the Janera Science lab results page and learn how to interpret one in our guide to reading a COA.

Every compound described here, Selank included, is supplied strictly for in-vitro laboratory research. Our research use only framework sets out what that means and who may purchase.

Frequently Asked Questions

What is Selank made of?

Selank is a synthetic heptapeptide with the sequence Thr-Lys-Pro-Arg-Pro-Gly-Pro. The first four residues are the natural tuftsin sequence, and the final three are a synthetic Pro-Gly-Pro tripeptide. Its molecular formula is C33H57N11O9 and its molecular weight is approximately 751.9 g/mol (PubChem, 2026).

How is Selank different from tuftsin?

Selank keeps the entire tuftsin tetrapeptide, Thr-Lys-Pro-Arg, and adds a Pro-Gly-Pro tripeptide to the C-terminus. That extension slows enzymatic breakdown, converting a short-lived natural fragment into a more stable molecule while preserving the original tuftsin sequence (Wikipedia, 2026).

Why does Selank contain Pro-Gly-Pro?

The Pro-Gly-Pro tripeptide is added to resist peptidase enzymes. Proline forms a rigid ring that creates steric hindrance against enzymes that would otherwise cleave the chain, which is why the extension is placed at the vulnerable C-terminal end of the peptide.

Is Selank related to Semax?

Both are heptapeptides developed through Russian molecular-genetics research, and both use the same Pro-Gly-Pro C-terminal extension for stability. Their parent sequences differ, since Selank is built on tuftsin and Semax on a fragment of adrenocorticotropic hormone, but the stabilization strategy is shared.

What have laboratory studies measured about Selank?

Published research in serum, cell, and animal models has reported inhibition of enkephalin-degrading enzymes, changes in the expression of inflammation-related genes including interferon-alpha in mouse spleen, and increases in BDNF messenger RNA and protein in rat hippocampus (Regulatory Peptides, 2011). These are laboratory findings and do not describe use in humans.

How is Selank purity verified?

Purity and identity are confirmed by high-performance liquid chromatography (HPLC) and mass spectrometry, with results recorded on a lot-specific Certificate of Analysis. Each lot supplied by Janera Science is independently tested before release.

Key Takeaways

• Selank is a synthetic tuftsin-derived heptapeptide with the sequence Thr-Lys-Pro-Arg-Pro-Gly-Pro, combining the four-residue tuftsin peptide with a synthetic Pro-Gly-Pro tail (PubChem, 2026).

• The Pro-Gly-Pro extension is the stabilizing feature, using proline's rigid ring to resist peptidases at the C-terminus of the chain.

• Selank preserves the intact tuftsin sequence, which carries the parent peptide's molecular recognition character into a longer, more durable molecule (Wikipedia, 2026).

• Selank and Semax share one stabilization strategy applied to different parent sequences, a pattern that runs through this family of research peptides.

• Published laboratory research spans several molecular systems, including enkephalin-degrading enzyme inhibition, inflammation-related gene expression, and BDNF expression (Doklady Biological Sciences, 2008).

All Janera Science compounds are supplied strictly for in-vitro laboratory research use only. They are not for human or veterinary use and have not been evaluated by the FDA.