Valine (Val, V)
Valine is a hydrophobic, beta-branched amino acid with an isopropyl side chain. It strongly favours beta-strand structure and is a common cause of aggregation and difficult couplings in peptide synthesis.
Structure and properties
Valine carries an isopropyl group attached directly to the beta carbon. This beta branching places bulk close to the backbone, restricting conformation and giving valine one of the strongest preferences for extended beta-strand structure. The side chain is entirely aliphatic and hydrophobic, so valine is often buried in protein cores or on the hydrophobic face of beta sheets. Valine is smaller than leucine and isoleucine but shares their non-polar character. Unlike isoleucine and threonine, it has only one stereocentre, because its two side-chain methyl groups are identical.
Role in peptides
Valine provides hydrophobic contact and beta-strand propensity. It is the C-terminal residue of KPV, the Lys-Pro-Val tripeptide derived from the C-terminus of alpha-MSH, and BPC-157 ends with leucine and valine. Valine is present in GLP-1 analogues such as semaglutide and in LL-37. In amyloid-forming and beta-hairpin peptides, valine-rich stretches drive strand pairing. Valine is often swapped with isoleucine or alanine in structure-activity studies to test the effect of side-chain size and branching.
Stability and analysis
Valine has few chemical stability concerns, as its side chain is inert. Its issues are mainly synthetic: beta branching slows couplings, and valine-rich sequences tend to aggregate on resin through beta-sheet formation, giving deletion impurities that may elute close to the target peak. Stronger coupling conditions, pseudoproline or backbone-protecting strategies are used to manage this. Hydrophobic valine-rich peptides can also be hard to dissolve for analysis.
In PeptideWiki compounds
Compounds whose sequence contains valine, with the number of occurrences.
- IGF-1 LR3 (4)
- Teriparatide (3)
- Thymosin α1 (3)
- AOD-9604 (2)
- LL-37 (2)
- Larazotide (2)
- Pramlintide (2)
- VIP (vasoactive intestinal peptide) (2)
- Abaloparatide (1)
- Afamelanotide (1)
- BPC-157 (1)
- CJC-1295 (1)
- Calcitonin (salmon) (1)
- Exenatide (1)
- Humanin (1)
- KPV (1)
- Sermorelin (1)
- Tesamorelin (1)
Frequently asked questions
Why is valine hard to couple in peptide synthesis?
The bulky isopropyl group sits right next to the reacting amine and carbonyl, hindering approach of the incoming activated amino acid. Coupling onto or with valine is therefore slower, and incomplete coupling leaves deletion sequences. Runs of valine and other beta-branched residues also promote beta-sheet aggregation of the growing chains on the resin, which further reduces reactivity. See the solid-phase synthesis guide for background.
Is valine an essential amino acid?
Yes. Humans cannot synthesise valine and must obtain it from the diet, which places it among the essential amino acids. Together with leucine and isoleucine it is one of the three branched-chain amino acids, which share related metabolic pathways. In a peptide context, whether an amino acid is essential has no bearing on its chemistry; it simply describes nutritional biosynthesis in humans.
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