One-to-Three Converter

How to convert one-letter amino acid codes to three-letter codes

Paste a one-letter protein sequence, or upload a .txt, .fasta, .fa, .fas, or .seq file, then choose the three-letter formatting you need. The converter maps each residue to its conventional abbreviation, such as M to Met and K to Lys, and returns copyable, downloadable plain text. FASTA headers can stay in place when converting one or more records.

For a short sequence, leave the default title case and hyphen delimiter selected:

Input
MKWV

Output
Met-Lys-Trp-Val

FASTA headers are retained by default. This multi-record example uses an uppercase, space-delimited output:

Input
>hemoglobin_fragment
MVLSP
>signal_peptide
MKWV

Output
>hemoglobin_fragment
MET VAL LEU SER PRO
>signal_peptide
MET LYS TRP VAL

Input

Use the 20 standard residue letters, plus the codes the converter recognizes for selenocysteine (U), pyrrolysine (O), asparagine or aspartic acid (B), glutamine or glutamic acid (Z), and an unknown residue (X). The converter does not remove punctuation, spaces, or other unrecognized characters from raw sequence text. Each unrecognized character becomes Unk in title case, or UNK or unk when another output case is selected.

When Preserve FASTA format is on, sequence lines are collected under their > headers, so wrapped input sequence lines are treated as one sequence. When it is off, do not include headers: the converter treats every character in the submitted text as sequence input.

Settings

Position-number example

For a fragment beginning at residue 42, select Show position numbers, Start and end, and Number every N amino acids set to 3:

Input
MKWVY

Output
   42 Met-Lys-Trp 44
   45 Val-Tyr 46

Results

One-letter and three-letter amino acid codes

The one-letter notation is compact enough for sequence databases, alignments, and FASTA files. Three-letter notation is often easier to read in teaching materials, mutation reports, structure annotations, and residue lists. This converter changes notation only. It does not translate DNA or RNA, infer codons, or modify the residue order.

Which protein sequence converter should I use?

FAQ

How do I convert an amino acid sequence from one-letter to three-letter code?

Paste the one-letter sequence, choose the delimiter and capitalization, then run the converter. With the defaults, ARND becomes Ala-Arg-Asn-Asp.

Can I convert a FASTA file from one-letter to three-letter amino acid codes?

Yes. Upload a supported text or FASTA file and leave Preserve FASTA format enabled. Header lines are retained, and every sequence record is converted separately.

What does the amino acid code X mean?

X denotes an unknown or unspecified amino acid. The converter renders it as Xaa, while B becomes Asx and Z becomes Glx for ambiguous acidic or amide residues.

Can I remove separators between three-letter amino acid codes?

Yes. Set Output delimiter to No delimiter. For example, MKWV becomes MetLysTrpVal.