Alanine (Ala, A)
Alanine is a small, non-polar amino acid with a methyl side chain. It is a strong helix former and the standard substitution used in alanine scanning studies of peptide function.
Structure and properties
Alanine carries a single methyl group as its side chain, making it the simplest chiral amino acid after achiral glycine. The side chain is small, non-polar and chemically inert, so it neither ionises nor takes part in hydrogen bonding. Because the methyl group removes conformational freedom without adding steric bulk, alanine strongly favours the alpha-helical region of backbone space. It is moderately hydrophobic and is tolerated both on protein surfaces and in buried cores. Natural proteins use the L-form; D-alanine occurs in bacterial cell walls and is sometimes introduced into synthetic peptides to slow proteolysis or alter conformation.
Role in peptides
In peptide design alanine is the default neutral residue. Alanine scanning, in which each position is replaced in turn by alanine, is a standard way to identify which side chains contribute to binding or activity. Alanine stabilises helices in short peptides and appears often in helical antimicrobial and incretin sequences. Its close relative, alpha-aminoisobutyric acid (Aib), adds a second methyl group: semaglutide replaces the native alanine at position 8 (GLP-1 numbering) with Aib to resist cleavage by dipeptidyl peptidase-4, which removes N-terminal dipeptides ending in Ala or Pro. Alanine is also present in epitalon (Ala-Glu-Asp-Gly).
Stability and analysis
Alanine raises few specific concerns. The side chain does not oxidise, deamidate or cyclise, and alanine couples efficiently in solid-phase synthesis. Analytical issues are generally those of neighbouring residues. Two points are worth noting: runs of alanine can promote helical or aggregated structure that broadens HPLC peaks, and the D-isomer is not distinguished from the L-isomer by mass spectrometry, so chiral purity, where it matters, needs chiral amino acid analysis or comparison with a reference standard.
In PeptideWiki compounds
Compounds whose sequence contains alanine, with the number of occurrences.
- IGF-1 LR3 (7)
- Tesamorelin (5)
- CJC-1295 (4)
- Pramlintide (3)
- Sermorelin (3)
- Thymosin α1 (3)
- Abaloparatide (2)
- BPC-157 (2)
- DSIP (2)
- Exenatide (2)
- GHRP-2 (2)
- Humanin (2)
- Thymosin β4 (2)
- VIP (vasoactive intestinal peptide) (2)
- ARA-290 (cibinetide) (1)
- Epitalon (1)
- GHRP-6 (1)
- Setmelanotide (1)
- Snap-8 (1)
Frequently asked questions
Why is alanine used in alanine scanning?
Alanine removes a side chain beyond the beta carbon without introducing new charge, bulk or unusual backbone flexibility. Replacing a residue with alanine therefore reports roughly what that side chain contributed to binding or activity, while leaving the backbone conformation largely intact. Glycine would add flexibility and proline would impose rigid constraints, so alanine is the most neutral practical substitute for this kind of mapping.
What is the difference between alanine and Aib?
Aib (alpha-aminoisobutyric acid) carries two methyl groups on the alpha carbon instead of one hydrogen and one methyl. It is achiral, more strongly helix-promoting than alanine, and resistant to many proteases. It is not one of the twenty genetically encoded amino acids. Several GLP-1 receptor agonists, including semaglutide and tirzepatide, use Aib near the N-terminus to block degradation by dipeptidyl peptidase-4.
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