Analyze biochemical and physical parameters of your protein sequences
Input Protein Sequence
Only standard amino acid characters are accepted.
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Our Protein Instability Index Calculator is a powerful, web-based tool for evaluating the stability of your protein sequences. By simply inputting a sequence, you can instantly compute its Instability Index, a critical parameter for predicting whether a protein will be stable in a test tube. This tool is essential for researchers in protein engineering, expression, and purification, as it helps identify potentially unstable proteins early, saving time and resources in downstream experiments.
How to Use
Analyzing your protein sequence is a simple, three-step process:
- Input Sequence: Paste your protein sequence into the text box. The sequence should contain only standard single-letter amino acid codes.
- Analyze: Click the “Analyze Sequence” button to process your data.
- Review Results: The tool will instantly display a comprehensive report of the calculated parameters for your protein, with a clear indication of its predicted stability.
Tip: Before pasting, ensure your sequence is in a plain text format and does not contain any headers, numbers, or non-standard characters for the most accurate results.
How is the Protein Instability Index Calculated?
The Instability Index provides an estimate of the stability of a protein in a test tube (in vitro). A protein with an Instability Index below 40 is predicted to be stable, while a value above 40 predicts that the protein may be unstable.
The calculation is based on the analysis of dipeptides (pairs of adjacent amino acids). Through statistical analysis of a large set of stable and unstable proteins, a specific weight value of instability was assigned to each of the 400 possible dipeptides.
The algorithm works by:
- Scanning your protein sequence from the N-terminus to the C-terminus.
- Identifying every dipeptide pair (e.g., the first and second amino acid, the second and third, and so on).
- Assigning the corresponding instability weight value to each pair.
- Summing these values and normalizing for the protein’s length to compute the final Instability Index.
This method allows for a reliable, sequence-based prediction of a protein’s inherent structural stability.
Features and Outputs
This protein parameters analyzer provides the following comprehensive outputs:
- Instability Index: Computes a score to predict the protein’s stability in a test tube. A value below 40 suggests a stable protein, while a value above 40 indicates potential instability.
- Amino Acid Composition: Delivers the absolute count and percentage frequency for each of the 20 standard amino acids in your sequence.
- Molecular Weight (MW): Calculates the protein’s molecular weight based on the average isotopic masses of its constituent amino acids.
- Theoretical Isoelectric Point (pI): Estimates the pH at which the protein carries no net electrical charge, a critical parameter for purification methods.
- Amino Acid Property Groups: Classifies and sums amino acids based on their chemical properties (e.g., Hydrophobic, Polar, Positively Charged, Negatively Charged).
- Atomic Composition: Provides the total count of each atom type (Carbon, Hydrogen, Nitrogen, Oxygen, Sulfur) that makes up the protein molecule.
- Extinction Coefficient: Estimates the molar absorption coefficient of the protein at 280 nm, essential for determining protein concentration via UV spectroscopy.
- Estimated Half-Life: Predicts the protein’s stability and lifespan within different biological systems, offering in-vitro estimates for mammalian reticulocytes, yeast, and E. coli.
- Aliphatic Index: Calculates the relative volume of the protein occupied by aliphatic side chains (Alanine, Valine, Isoleucine, and Leucine), a positive indicator of thermostability.
- Grand Average of Hydropathicity (GRAVY): A score representing the overall hydrophobicity of the protein. Positive values indicate a more hydrophobic protein, while negative values suggest a more hydrophilic one.
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References & Suggested Reading
This tool was developed in line with established principles in computational biochemistry for accurate, reliable results. The resources listed below are the foundational research and key papers that define these standards, and we highly recommend them for a deeper understanding of the scientific principles.
- Gasteiger, E., Hoogland, C., Gattiker, A., Duvaud, S., Wilkins, M. R., Appel, R. D., & Bairoch, A. (2005). Protein identification and analysis tools on the ExPASy server. In J. M. Walker (Ed.), The Proteomics Protocols Handbook (pp. 571–607). Humana Press. https://doi.org/10.1385/1-59259-890-0:571
- Gamage, D. G., Gunaratne, A., Periyannan, G. R., & Russell, T. G. (2019). Applicability of instability index for in vitro protein stability prediction. Protein and peptide letters, 26(5), 339-347. https://doi.org/10.2174/0929866526666190228144219
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.