Chemistry & nose-to-brain delivery
Selank's structure is short and proline-rich: seven amino acids, three of them prolines, with the last three added, in…
Seven residues, three prolines, and a path to the brain
Selank's structure is short and proline-rich: seven amino acids, three of them prolines, with the last three added, in its designers' words, to enhance metabolic stability and the length of action. It is given intranasally, a route that a review describes as reaching the brain directly along the olfactory and trigeminal nerves. This unit shows the molecule and follows it from nasal drops toward its target.
It also confronts an inconvenient gap: how much of an intranasal dose ends up in brain tissue is not stated in any source this course cites, which is why "put in the nose" is not the same as "delivered to the brain."
Key terms
The molecule, residue by residue
Selank's sequence is Thr-Lys-Pro-Arg-Pro-Gly-Pro: the tuftsin core (Thr-Lys-Pro-Arg) followed by the Pro-Gly-Pro tail its designers added to improve metabolic stability. The registered 0.15% nasal drops contain it as the diacetate salt. Its sibling semax, Met-Glu-His-Phe-Pro-Gly-Pro, ends in the same three residues. Click each building block (residue) to see its role; the standout feature is the three prolines.
The structure frames the pharmacology. The first four residues are tuftsin, carrying the immune heritage; the last three are the added tail. Proline's rigid ring blocks many of the enzymes that cut small peptides, which is the general chemistry the designers were relying on when they added it, though how much durability it actually bought is not measured in any source cited here.
AdvancedWhy three prolines matter so much
Proline is the only amino acid whose side chain loops back to its own backbone nitrogen, forcing a kink and removing the amide hydrogen that many proteases recognize. That is general peptide chemistry, and it is the reasoning behind the Pro-Gly-Pro design, which its authors describe as elongating the tuftsin fragment to enhance metabolic stability and the length of action. What no cited source provides is the payoff measured: neither tuftsin's stability nor Selank's has been quantified here.