What is Selank?

Selank is a synthetic heptapeptide with the sequence Thr-Lys-Pro-Arg-Pro-Gly-Pro, also written as TKPRPGP. This means it is a molecule made up of seven linked amino acid residues. Its characteristic feature is the combination of a sequence corresponding to tuftsin with the terminal Pro-Gly-Pro segment. [1,2]

The most important information about Selank concerns precisely this structure. The name refers to a specific peptide, not to an entire group of substances with a similar purpose. Understanding its sequence makes it possible to distinguish it from tuftsin, shorter fragments and modified derivatives.

Below we present basic information about Selank: its composition, formulation, relationship to tuftsin and the meaning of the most frequently encountered names. Chemical terms are explained upon first use.

What exactly is Selank?

Selank belongs to the short peptides. The term „heptapeptide” indicates that its chain contains seven amino acid residues. An amino acid residue is simply an amino acid that is already part of a connected chain.

„Synthetic” means that the compound is obtained via chemical synthesis. In the case of Selank, the reference point for its structure is tuftsin. However, this does not mean that the finished Selank is isolated from tuftsin, nor that the two peptides are identical.

In the literature, Selank also appears under the designation TP-7. A 2002 paper concerning Selank and tuftsin derivatives documents this direction of research conducted in Russia. This is information regarding the scientific history of the compound, and not proof of its natural occurrence. [3]

What is the amino acid sequence of Selank?

The sequence of Selank can be represented in two equivalent notations:

• Three-letter code: Thr-Lys-Pro-Arg-Pro-Gly-Pro.
• Single-letter notation: TKPRPGP.

Both show the same elements in the same order. The longer notation makes it easier to recognise amino acid names, whereas the shorter one takes up less space in tables and databases. [1]

Position in Selank	Shortcut	Letter	Amino acid
1	Three	T	Threonine
2	Lys	K	Lysine
3	Pro	P	Proline
4	Arg	R	Arginine
5	Pro	P	Proline
6	Gly	G	Glycine
7	Pro	P	Proline

Sequence reading reveals that proline appears three times, and each of the other mentioned amino acids once. Selank therefore contains seven residues representing five types of amino acids.

The mere list of these ingredients is not enough to describe Selank. Their arrangement matters. A chain built from the same amino acids, but linked in a different order, would describe a different peptide.

What links Selank with tuftsin?

Tuftsin is a tetrapeptide, meaning a peptide containing four amino acid residues. Its sequence is Thr-Lys-Pro-Arg, abbreviated as TKPR. The same segment is found at the beginning of Selank. [2]

Comparison of both sequences shows the difference without the need for detailed chemistry knowledge:

Peptide	Sequence	Number of remainders
Tuftsin-A	Thr-Lys-Pro-Arg	4
Selank	Thr-Lys-Pro-Arg-Pro-Gly-Pro	7

Selank can therefore be described as a chain-elongated tuftsin analogue. The word „analogue” here means a compound that is structurally related, but differs in its makeup. It is not a synonym for the word „copy”.

The additional three residues become part of a single molecule. Selank is not a mixture of tuftsin and a separate tripeptide. This is an important distinction: the co-presence of two peptides in a sample does not imply the formation of a chain corresponding to Selank.

What does the final fragment Pro-Gly-Pro mean?

Pro-Gly-Pro, PGP for short, occupies positions five to seven in Selank. It is therefore the terminal segment of its sequence. The term „tripeptide” refers to three linked residues of proline, glycine and proline.

In the structural description, the TKPR and PGP parts can be separated to more easily see the relationship with tuftsin. This kind of division is a way of explaining the structure. It does not mean that the finished molecule consists of two loose components.

The presence of the PGP should not be treated as independent proof of a specific stability of Selank either. The statement that the modification increases stability requires indicating a comparison and measurement conditions. The mere knowledge of the final three letters does not allow the degradation time of the entire peptide to be stated.

Similarly, the result concerning the isolated PGP fragment does not automatically describe the full Selank. The fragment can be a separate subject of study, so its name must be retained when discussing the results.

How to understand the full record of Selanko?

In the PubChem database, Selank is also represented as H-Thr-Lys-Pro-Arg-Pro-Gly-Pro-OH. The initial H and final OH describe the terminals of the molecule; they are not additional amino acids. [1]

The sequence is read from the amino end, designated as N, to the carboxyl end, designated as C. In Selank, threonine is at the beginning and proline is at the end.

This explanation helps avoid a common misunderstanding: the longer notation with end markers still refers to the heptapeptide. It does not change the number of residues in the chain.

If the documentation indicates an additional modification of the terminus, it must be included separately. The TKPRPGP entry alone may not suffice to fully describe such a derivative, as it primarily shows the amino acid sequence.

Empirical formula and mass of Selank

For the basic structure of Selank, PubChem gives the formula C₃₃H₅₇N₁₁O₉ and a molar mass of approximately 751.9 g/mol. The compound has the PubChem CID 11765600 and CAS number 129954-34-3. [1]

The molecular formula indicates the number of carbon, hydrogen, nitrogen and oxygen atoms in the described molecule. The sequence answers a different question: it shows the order of amino acid residues. Both pieces of information complement each other, but are not interchangeable.

The given molar mass is a chemical parameter. It does not specify the quantity intended for use or the content of any sample described by the name Selank.

If the material also contains counterions, water or other components, its total composition requires a separate description. This does not change the reference sequence, but is important when interpreting data about the material.

Selank, TP-7 and derivatives – how to distinguish the names?

The designation TP-7 can be found in literature concerning the tuftsin analogue. When searching for older publications, it is worth including both terms and then checking what material the authors actually described. [3]

A different situation occurs when information about a chemical modification is added to the name of Selank. Such an addition should not be omitted. It can distinguish a derivative from the base peptide.

Also, „Selank fragment” is a broader term than „Selank”. It indicates a part of its structure, and not automatically the entire seven-element chain. Publications about the full peptide and its fragments should be distinguished at the nomenclature level already.

What information belongs to the basic description of Selank?

The most useful description of Selank combines the name, the full sequence and information about its relationship with tuftsin. Thanks to this, the reader knows which molecule is the subject of the article.

Data on potential mechanisms or experimental results require separate discussion. They do not stem directly from the number of amino acids or from the shared fragment with another peptide. Structural similarity helps to formulate a research question, but does not replace the answer obtained in the study.

Therefore, terms suggesting memory enhancement, anxiety reduction or immune support are not the chemical definition of Selank. In the introductory article, its identity can be explained without attributing expected results of use to it.

Frequently asked questions about Selank

Why is Selank called a heptapeptide?

Because its chain contains seven amino acid residues. The prefix „hepta-” refers precisely to this number. The name determines the length of the peptide, whereas its identity requires providing the sequence. Other heptapeptides exist, so merely stating that the compound has seven residues is not enough to identify Selank.

Are Selank and tuftsin the same peptide?

No. Tuftsin corresponds to the first four residues of the Selank sequence, and Selank additionally contains the terminal Pro-Gly-Pro segment. These are related but distinct structures. Information concerning one peptide should not be automatically attributed to the other. The shared beginning of the sequence explains their relationship, not full equivalence.

Is TKPRPGP a different type of Selank?

No. It is a shorter way of writing the sequence Thr-Lys-Pro-Arg-Pro-Gly-Pro. Each letter represents a specific amino acid at a given position. Both notations represent the same order of residues. The difference lies in the way the information is presented, much like the full name and its established abbreviation.

Does Selank contain seven different amino acids?

No. It contains seven residues, but five types of amino acids, because proline repeats three times. The number of residues refers to the chain's length, whereas the number of types describes its composition. This distinction helps to read the sequence table correctly and avoids treating every position as a different amino acid.

Is Pro-Gly-Pro the same as Selank?

No. PGP only constitutes the final part of the Selank sequence. The full peptide also includes the preceding segment corresponding to tuftsin. Therefore, studying the fragment on its own is not studying the identical molecule. When reading publications, it matters whether the authors analysed the full chain or the selected shorter segment.

Does the synthetic origin change the name of Selank?

Synthetic origin describes the method of obtaining a compound. The name Selank refers to a specific structure that the synthesis is intended to reproduce. However, this does not mean that the mere declaration of the name confirms the composition of the sample. The description of the molecule and the results concerning a specific material remain separate pieces of information.

Is the empirical formula alone sufficient to describe Selank?

It does not present all structural details. It informs about the number of atoms of individual elements, but does not show the order of amino acids as directly as the sequence. Therefore, in a basic description, it is worth providing both types of data. Each answers a different question about the same molecule.

Can the name TP-7 appear in publications about Selank?

Yes, this designation is found in the literature concerning this tuftsin analogue. It helps to locate papers that do not use the name Selank exclusively. However, finding a common name is only the beginning: before comparing results, one should check the description of the peptide under study, its possible modifications, and the scope of the experiment. [3]

Disclaimer

The article is educational in nature and concerns the chemical identity and nomenclature of Selank. It does not constitute medical advice or a recommendation to purchase or use. It does not contain instructions for the preparation, dosage or administration of the peptide. Information regarding the structure does not confirm the safety or quality of any specific material.

For research purposes only: The Selank products offered by Semax Polska are intended solely for laboratory and scientific research. They are not intended for human consumption or for use in the diagnosis, treatment, prevention or alleviation of any diseases. Researchers should comply with all applicable regulations and institutional guidelines regarding the handling of research peptides.

References

[1] National Center for Biotechnology Information. PubChem Compound Summary for CID 11765600, Selank. Selank's record in PubChem.

[2] National Center for Biotechnology Information. PubChem Compound Summary for CID 156080, Tuftsin. PubChem substance record.

[3] Kozlovskaia, M. M., Kozlovskiĭ, I. I., Val’dman, E. A., & Seredenin, S. B. (2002). [Selank and short peptides of Taftsin derivatives in regulation of adaptive behaviour of animals in stress]. Ross Fiziol Zh Im I M Sechenova, 88(6), 751–761. PMID: 12154572. PubMed publication record.

[4] PubChem. (2026). Selank Compound Summary. National Centre for Biotechnology Information, National Library of Medicine. https://pubchem.ncbi.nlm.nih.gov/compound/Selank