Instability Index Calculator

Calculate the instability index of protein sequences to predict their stability.

What is Instability Index?

The instability index (II) provides an estimate of protein stability in a test tube. It is based on the statistical analysis of stable and unstable proteins.

Interpretation

• II < 40: Protein is predicted to be stable
• II >= 40: Protein is predicted to be unstable (short half-life in vitro)

How It Works

The instability index is calculated based on the dipeptide composition of the protein, using experimentally determined instability weight values for each dipeptide.

Input

• Protein sequences: Enter one or more protein sequences in FASTA format
• Supports batch processing of multiple sequences

Output

• Protein ID: Identifier from FASTA header
• Number of Amino Acids: Sequence length
• Instability Index: II value (lower is more stable)

Use Cases

• Screen protein variants for expression
• Predict shelf-life of recombinant proteins
• Guide protein engineering efforts
• Identify stabilizing mutations