Molecular File Converter
Convert between chemical file formats with our web-based tool
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Our PDB to FASTA Converter is a simple and efficient web-based tool designed to extract protein or nucleic acid sequences from 3D structural data. It reads atomic coordinate files in the Protein Data Bank (PDB) format and converts them into the FASTA format, which represents the primary amino acid or nucleotide sequence.
This conversion is a crucial first step for a wide range of bioinformatics tasks, including multiple sequence alignment, phylogenetic analysis, and sequence database searches such as BLAST. This tool streamlines your workflow, allowing you to move quickly from structural data to sequence-based analysis.
How to use (step-by-step)
Follow these simple steps to convert your file in seconds.
- Choose Your Formats: Use the “Input Format” and “Output Format” dropdown menus to select the conversion you need. Ensure PDB (Protein Data Bank format) is selected as the input and FASTA (FASTA format) as the output.
- Upload Your File: Click “Upload File” or drag and drop your file directly into the designated area. You can also paste the file’s content using the “Paste Content” option.
- Start the Conversion: Press the “Convert File” button to begin the process. The tool will process your file instantly.
- Download Your File: Once the conversion is complete, a download link for your new file will appear. Click it to save the FASTA file to your device.
Tip: If you encounter an error during conversion, check the Troubleshooting Guide section below—common causes and fixes are listed.
Input, Output, and Key Changes
Understanding the transformation from a PDB structure to a FASTA sequence is essential for bioinformatics analysis. Here’s a breakdown of the formats and the changes that occur.
Sample input (PDB Format)
The PDB format is a standard for representing the 3D coordinates of atoms in large biological molecules like proteins and nucleic acids. It provides a detailed structural view but is not suitable for sequence-based comparisons.
Example of a PDB file:
ATOM 1 N MET A 1 27.222 18.238 35.532 1.00 28.80 N
ATOM 2 CA MET A 1 27.989 17.078 35.048 1.00 28.80 C
ATOM 3 C MET A 1 27.213 16.035 34.341 1.00 28.80 C
ATOM 4 O MET A 1 26.009 16.121 34.221 1.00 28.80 O
ATOM 5 CB MET A 1 29.130 17.483 34.113 1.00 28.80 C
ATOM 6 N ALA A 2 27.920 15.050 33.890 1.00 26.54 N
ATOM 7 CA ALA A 2 27.288 13.970 33.208 1.00 26.54 C
Sample Output (FASTA Format)
The FASTA format is a text-based format for representing nucleotide or peptide sequences. It uses single-letter codes and begins with a description line, making it ideal for sequence databases and analysis tools.
Example of the corresponding FASTA file:
>1A4Y_A|Chains A|Trypsin|Bos taurus (9615)
MA...
(The full sequence is omitted for brevity)
Key Changes in the Conversion Process
The conversion from PDB to FASTA focuses on extracting the essential biological sequence:
- Sequence Extraction: The primary change is the extraction of the amino acid or nucleotide sequence. The tool reads the
ATOMrecords, identifies the residue name (e.g., MET, ALA), and converts it into its standard one-letter code (M, A). - Header Generation: A descriptive header line, starting with a “>” symbol, is created. This header typically includes the PDB ID and chain identifier (e.g.,
>1A4Y_A) to maintain a clear link to the source structure. - Handling of Multiple Chains: If the input PDB file contains multiple polypeptide or polynucleotide chains (e.g., Chain A, Chain B), the tool will generate a separate FASTA entry for each chain, allowing you to analyze them individually.
- Exclusion of Non-Standard Data: All non-essential information, such as atomic coordinates, temperature factors, and heteroatoms (
HETATMrecords like water molecules or ligands), is discarded to produce a clean sequence file.
Compatible Software
The generated FASTA files are ready to be used with a wide array of leading bioinformatics software and web servers:
- BLAST (Basic Local Alignment Search Tool)
- Clustal Omega
- MAFFT (Multiple Alignment using Fast Fourier Transform)
- T-Coffee
- Jalview
- MEGA (Molecular Evolutionary Genetics Analysis)
Troubleshooting Guide
Encountering an error can be frustrating, but most issues are easy to fix. Here are the most common problems you might face and how to resolve them.
General Tool Errors
Error: “Processing timed out”
- Why it happens: The conversion for your molecule is taking too long. This is rare for PDB to FASTA conversion but could occur with exceptionally large and complex PDB files.
- How to fix: Check that your file is correctly formatted. If the issue persists with a valid, large file, please contact us to discuss options.
Error: “CAPTCHA validation failed”
- Why it happens: Our system uses a CAPTCHA to prevent automated bots. This error occurs if the CAPTCHA was not solved correctly or timed out.
- How to fix: Simply reload the page and solve the new CAPTCHA.
Conversion-Specific Errors
These errors relate to the scientific data within your PDB file.
Error: “Output is empty” or “No sequence found”
- Why it happens: The input PDB file does not contain any standard amino acid or nucleotide residues in its
ATOMrecords. This can occur if the file only contains solvent, ions, a ligand (HETATM), or has a non-standard structure. - How to fix: Ensure your PDB file contains at least one standard protein or nucleic acid chain. Open the file in a text editor or molecular viewer to verify its contents.
Error: “Unrecognized residue name”
- Why it happens: The PDB file contains non-standard three-letter residue codes that the converter cannot map to a standard one-letter code (e.g., modified amino acids).
- How to fix: Manually edit the PDB file to replace non-standard residue names with their standard equivalents (e.g., change
MSEtoMETif appropriate for your analysis). Alternatively, remove these residues if they are not part of the main sequence you wish to extract.
Error: “Unexpected number of sequences in output”
- Why it happens: This is not a strict error, but a common source of confusion. Your input PDB file contained multiple chains (e.g., A, B, C), and the tool generated a separate FASTA sequence for each one.
- How to fix: This is the correct behavior. You can either use the specific sequence you need or combine them in a text editor if your goal is a single concatenated sequence. Check your PDB file in a viewer like PyMOL or UCSF Chimera to see how many distinct chains it contains.
If your problem isn’t listed here, we want to know about it! Please help us improve the tool by reporting the issue.
FAQ
References & Suggested Reading
This tool was developed in line with established principles in bioinformatics and computational biology. The resources listed below are foundational research and key papers that define the standards for PDB and FASTA formats, and we highly recommend them for a deeper understanding of the scientific principles.
- Berman, H. M., Westbrook, J., Feng, Z., Gilliland, G., Bhat, T. N., Weissig, H., Shindyalov, I. N., & Bourne, P. E. (2000). The Protein Data Bank. Nucleic Acids Research, 28(1), 235–242. https://doi.org/10.1093/nar/28.1.235
- O’Boyle, N. M., Banck, M., James, C. A., Morley, C., Vandermeersch, T., & Hutchison, G. R. (2011). Open Babel: An open chemical toolbox. Journal of Cheminformatics, 3(1), 33. https://doi.org/10.1186/1758-2946-3-33
- Sievers, F., & Higgins, D. G. (2018). Clustal Omega for making accurate alignments of many protein sequences. Protein Science, 27(1), 135–145. https://doi.org/10.1002/pro.3290
Meet the Authors
Mahdi Morshedi Yekta
Founder & Bioinformatics Developer
Mahdi is the founder of ScienceCodons and a Medical Biotechnologist with a deep passion for computational biology. Holding an M.Sc. in Medical Biotechnology, he specializes in transforming complex biological algorithms into accessible, high-performance web tools, bridging the gap between laboratory sciences and software engineering.
Fatemeh Faryadras
Medical Biotechnologist & Researcher
Fatemeh is a Medical Biotechnologist and researcher. With extensive expertise in genetic engineering, molecular cloning, and cancer biology, she combines her rigorous laboratory background with intuitive design principles to create reliable, user-centered scientific calculators and tools.
Dr. Mosayeb Rostamian
Assistant Professor, Infectious Diseases Research Center
Certified Scientific Reviewer
Google ScholarExpert Review Process
To ensure the highest quality and scientific accuracy, this tool's underlying algorithms, formulas, and edge-case handling have been thoroughly reviewed and validated by Dr. Mosayeb Rostamian.
The "Reviewed By" badge signifies that an independent expert has evaluated the tool's logic to guarantee accuracy and alignment with the current consensus in the scientific community.