Protein Solubility Calculator

Protein Solubility Calculator. A protein's solubility depends on how far the solution pH sits from its isoelectric point (pI) — the pH at which it carries no net charge and is most likely to aggregate. Enter your protein pI (or paste a FASTA sequence to calculate it), along with your solution pH, salt concentration, temperature, and any additives like detergents or reducing agents to get a Solubility Score out of 100. Secondary outputs include ΔpH, aggregation risk, and ionic strength. Also try the Activation Energy (Arrhenius) Calculator.

Calculation Method *

I know the protein's pI (fast)Calculate pI from sequence

Protein pI *

Protein Sequence (FASTA format)

Solution pH *

Salt Concentration *

Salt Unit *

Temperature *

Temperature Unit *

Protein Concentration (optional)

Concentration Unit

Detergent/surfactant present (e.g., Tween)

Reducing agent present (e.g., DTT/βME)

Glycerol present

Results

Solubility Score

ΔpH (pH - pI)

Aggregation Risk

Ionic Strength

Temperature

What is the isoelectric point (pI) and why is it important for solubility?

The isoelectric point is the pH at which a protein has zero net charge. Near the pI, proteins often aggregate and have poor solubility because they lack electrostatic repulsion. Moving the pH away from the pI improves solubility. See also our calculate Estimated Molecular Weight, Relative Front (Rf) Value & Confidence Level — SDS-PAGE Molecular Weight Estimator.

How does salt concentration affect protein solubility?

Salt concentration has complex effects on protein solubility. Low salt can destabilize proteins through charge-charge interactions, while moderate salt (50-200 mM) often stabilizes proteins. Very high salt concentrations can cause precipitation through salting-out effects.

What temperature should I use for protein storage and formulation?

Lower temperatures generally improve protein stability and solubility by reducing thermal motion and aggregation. Most proteins are stable at 4°C for storage, while room temperature (20-25°C) is common for formulation studies.

How accurate is this solubility prediction?

This calculator provides a relative solubility score based on key physicochemical factors. It's useful for comparing conditions and identifying potential problems, but experimental validation is always recommended for critical applications.

What additives can improve protein solubility?

Common additives include detergents (prevent aggregation), reducing agents like DTT (prevent disulfide crosslinking), and glycerol (stabilizes protein structure). The calculator accounts for these common additives in its scoring.

Can I use this calculator for recombinant proteins expressed in E. coli?

Yes, this calculator works for recombinant proteins. However, be aware that E. coli expression may result in inclusion bodies or misfolding, which affects solubility beyond what this calculator predicts based on sequence alone.

What should I do if my protein has a low solubility score?

Try adjusting the pH further from the pI, lowering the temperature, optimizing salt concentration, or adding stabilizing additives. Consider buffer optimization, protein engineering, or co-expression with chaperones for difficult proteins.

How do I interpret the ΔpH value?

ΔpH = pH - pI shows how far your solution pH is from the protein's isoelectric point. Values near zero indicate higher aggregation risk. Generally, |ΔpH| > 1.0 provides better solubility due to increased net charge. You might also find our calculate R² (Correlation Coefficient), Slope & Y-Intercept — Calibration Curve useful.