Chemistry & nose-to-brain delivery
Selank's properties are written into its structure: seven amino acids, three prolines that stiffen the chain and resist…
Seven residues, three prolines, and a path to the brain
Selank's properties are written into its structure: seven amino acids, three prolines that stiffen the chain and resist enzymes, and an intranasal route that gives partial direct access to the brain. This unit shows the molecule and follows it from a nasal spray to its target.
It also confronts an inconvenient number: only a small fraction of an intranasal dose actually reaches the brain, which is why "sprayed on 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. Click each building block (residue) to see its role. The standout feature is the three prolines at positions 3, 5, and 7, which stiffen the chain and make it hard for enzymes to cut.
The structure explains the pharmacology. The first four residues are tuftsin, preserving immune heritage; the last three are the protease-resistant tail. The three prolines are the reason Selank survives long enough to work, because proline's rigid ring blocks the enzymes that would otherwise shred a small peptide in minutes.
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. Three prolines spaced through a seven-residue peptide impose beta-turn-like constraints and create multiple protease-resistant points. This is why Selank, despite being tiny, is far more stable than native tuftsin, and it is the structural payoff of the Pro-Gly-Pro design.