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Amino acid code converter

Three-letter to one-letter amino acid codes and back. Plain text or FASTA.

Result
Three-letter to one-letter amino acid code
Protein sequences are written either with three-letter abbreviations (Met-Ala-Gly) or with the one-letter IUPAC code (MAG). Databases, alignment programs and FASTA files use one letter per residue; papers, peptide catalogues and mutation names such as p.Gly12Asp often use three. This converter goes both ways and keeps FASTA header lines as they are.
Worked example. Met-Ala-Gly-Trp-Ter becomes MAGW*. In the other directionMKWVTF becomes Met-Lys-Trp-Val-Thr-Phe.
Amino acid codes table
Amino acid3-letter1-letterAmino acid3-letter1-letter
AlanineAlaALeucineLeuL
ArginineArgRLysineLysK
AsparagineAsnNMethionineMetM
AspartateAspDPhenylalaninePheF
CysteineCysCProlineProP
GlutamineGlnQSerineSerS
GlutamateGluEThreonineThrT
GlycineGlyGTryptophanTrpW
HistidineHisHTyrosineTyrY
IsoleucineIleIValineValV
Asp or AsnAsxBGlu or GlnGlxZ
SelenocysteineSecUPyrrolysinePylO
Leu or IleXleJAny / unknownXaaX
The full table with side-chain properties and masses is on theamino acid table page.
How the input is read
  • Upper and lower case are both accepted: ALA, Ala and ala are the same residue.
  • Hyphens, spaces, line breaks and position numbers are ignored, so numbered sequences from papers or GenBank can be pasted as they are.
  • A stop is * in one-letter code and Ter in three-letter code.
  • Anything that is not a valid code is skipped and listed under the input.
To get a protein sequence from DNA, use the DNA to protein translator.
Frequently asked questions
How do I convert three-letter amino acid codes to one-letter codes?
Paste the sequence, for example Met-Ala-Gly-Trp or MetAlaGlyTrp. Each three-letter code is replaced by its single letter, giving MAGW. Hyphens, spaces, line breaks and numbering are ignored, and FASTA headers are kept.
What are Asx, Glx and Xaa?
Asx (B) means aspartate or asparagine, Glx (Z) means glutamate or glutamine, and Xaa (X) is any or an unknown residue. They appear when the method could not tell the two apart, for example after acid hydrolysis. Xle (J) means leucine or isoleucine.
What is the one-letter code for selenocysteine and pyrrolysine?
Selenocysteine is Sec or U, and pyrrolysine is Pyl or O. They are the 21st and 22nd genetically encoded amino acids.
How is a stop codon written?
As an asterisk (*) in one-letter code and as Ter in three-letter code. The converter also reads Stp, End and *** as a stop.
Why are some of my residues reported as not recognised?
In three-letter mode the input is read three letters at a time. A typing error such as Gyl shifts nothing, it is reported and skipped, and reading continues with the next three letters. If the total letter count is not a multiple of three, the leftover letters are reported as well.