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 text, FASTA, Word or PDF file. MKWV becomes Met-Lys-Trp-Val with the default title case and hyphen delimiter. Conversion runs in the browser and returns copyable text and a downloadable .txt file. FASTA headers are retained by default.

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

Spaces, wrapped lines and position numbers at the ends of sequence lines are formatting rather than residues. This pasted fragment produces the same five residues as MKWVY:

Input
1 MK WV 4
5 Y 5

Output
Met-Lys-Trp-Val-Tyr

Input

Uppercase and lowercase input are accepted. The recognized alphabet includes the 20 standard residues, selenocysteine (U), pyrrolysine (O), ambiguous residues (B, Z, J) and an unknown residue (X). For example, BZXJOU becomes Asx-Glx-Xaa-Xle-Pyl-Sec, using the INSDC amino acid abbreviations.

Whitespace, invisible document characters and leading list bullets are removed from sequence lines. Position numbers separated from residues by whitespace, including number-only rulers, are removed. Other characters, including alignment gaps (-, .) and stop markers (*), retain the earlier behavior: each becomes Unk, UNK or unk. The preview summary reports replacements; the run log records formatting cleanup and the warning.

Only a > header separates records. Header-free lines are joined into one sequence, so put names such as GFP on FASTA headers. A name made entirely of amino acid letters cannot be distinguished from a sequence. Tables, name:sequence rows, annotated sequence files, structure files and FASTQ input need conversion to protein FASTA first.

When Preserve FASTA format is on, headers remain exactly as submitted and wrapped sequence lines are collected under each header. Turning it off removes headers while keeping each record on separate output lines. It never converts names into residues. Existing empty FASTA records retain their headers when enabled, but an input containing no residue positions returns an error.

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 5:

Input
MKWVYARN

Output
   42 Met-Lys-Trp-Val-Tyr 46
   47 Ala-Arg-Asn 49

Results

Preview opens first, followed by Files and Logs. Check any replacement notice in the preview summary before using the converted text. Unk is a replacement for unsupported input, whereas Xaa represents an explicit X in the original sequence.

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.

What does J mean in an amino acid sequence?

J denotes leucine or isoleucine and converts to Xle. It remains an ambiguous residue rather than choosing either Leu or Ile.

Why does my output contain Unk?

An unsupported character was replaced. Gaps, stop markers and punctuation become Unk, and the result warning reports their count. Whitespace and position numbers at line ends do not create residues.

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

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