The one-letter amino acid code
Peptide sequences are written compactly using one-letter codes for the twenty standard
amino acids. The sequenceShort field in each entry uses this notation, and it is what the
fingerprint and residue search are built on.
| Code | 3-letter | Amino acid | Class | | :--: | :------: | ---------- | ----- | | A | Ala | Alanine | Nonpolar | | R | Arg | Arginine | Basic (+) | | N | Asn | Asparagine | Polar | | D | Asp | Aspartic acid | Acidic (−) | | C | Cys | Cysteine | Polar | | E | Glu | Glutamic acid | Acidic (−) | | Q | Gln | Glutamine | Polar | | G | Gly | Glycine | Nonpolar | | H | His | Histidine | Basic (+) | | I | Ile | Isoleucine | Nonpolar | | L | Leu | Leucine | Nonpolar | | K | Lys | Lysine | Basic (+) | | M | Met | Methionine | Nonpolar | | F | Phe | Phenylalanine | Nonpolar | | P | Pro | Proline | Nonpolar | | S | Ser | Serine | Polar | | T | Thr | Threonine | Polar | | W | Trp | Tryptophan | Nonpolar | | Y | Tyr | Tyrosine | Polar | | V | Val | Valine | Nonpolar |
The class column is a simplification. Histidine in particular sits near neutral pH and is sometimes grouped differently; cysteine and tyrosine have nuances too. Use the classes as a visual aid, not a substitute for a chemistry reference.
Writing a sequence
Read sequences N-terminus to C-terminus, left to right. For example, the copper tripeptide
GHK is glycine–histidine–lysine. Non-standard residues (D-amino acids, modifications, or a
bound metal) don't have one-letter codes — note them in the human-readable sequence field and
the body instead.