1. What is ExPASy Protein MW Calculator?

The ExPASy Protein Molecular Weight Calculator retrieves the molecular weight of a protein by querying the ExPASy (Expert Protein Analysis System) database using the protein name.

2. How Does the Calculator Work?

The calculator performs a lookup in the ExPASy database:

Where:

• \( protein\_name \) — Standard name or accession number of the protein
• \( MW \) — Molecular weight in g/mol

Explanation: The calculator queries the ExPASy database which contains curated information about proteins including their molecular weights.

3. Importance of Molecular Weight Calculation

Details: Knowing a protein's molecular weight is essential for laboratory techniques like SDS-PAGE, mass spectrometry, chromatography, and protein quantification.

4. Using the Calculator

Tips: Enter the standard protein name or UniProt accession number. For best results, use official protein names or accession codes.

5. Frequently Asked Questions (FAQ)

Q1: What protein naming conventions work best?
A: Official gene names (e.g., "TP53") or UniProt accession numbers (e.g., "P04637") give the most reliable results.

Q2: Does this calculate or look up molecular weight?
A: It looks up the molecular weight from curated data rather than calculating it from sequence.

Q3: What if my protein isn't found?
A: Try alternative names or accession numbers. Some newly discovered proteins may not be in the database yet.

Q4: Are post-translational modifications considered?
A: The database typically provides the molecular weight of the unmodified canonical sequence.

Q5: Can I get weights for protein complexes?
A: This tool is for single proteins. Complex molecular weights would need to be calculated separately.