Calculate the theoretical pI (isoelectric point) for protein sequences. Predict protein charge at different pH values.
Paste one or more FASTA sequences (max 200,000,000 characters).
Number of copies of the protein tag to add.
Common protein tags to append to the sequence.
Select the pK value set for isoelectric point calculation.
Paste one or more protein sequences in FASTA format. Non-protein characters are automatically filtered (limit 200 million characters).
Select common epitope tags (FLAG, HA, His6, MBP, GST, etc.) and specify the number of copies to append. This calculates the pI of the tagged fusion protein.
Select EMBOSS (standard research pK values) or DTASelect (proteomics-oriented pK values). Different sets may yield slightly different pI predictions.
Results show the theoretical isoelectric point where the protein has zero net charge. Use this for isoelectric focusing experiments and protein purification planning.
The isoelectric point (pI) is the pH at which a protein carries no net electrical charge. At the pI, the number of positive charges equals the number of negative charges, making the protein least soluble in aqueous solutions and most prone to precipitation.
Isoelectric focusing uses the pI to separate proteins in a pH gradient. Proteins migrate through the gradient until they reach their pI, where they stop moving. This technique is useful for protein purification and analysis on 2-D gels.
EMBOSS: Uses pK values from the EMBOSS bioinformatics package. More commonly used in research.
DTASelect: Uses pK values from DTASelect (a proteomics tool). Alternative set for comparison.
Common epitope tags (FLAG, HA, His6, etc.) can be appended to sequences to calculate the combined pI of the fusion protein. This is useful for predicting protein behavior during purification.