Analyze biochemical and physical parameters of your protein sequences
Input Protein Sequence
Only standard amino acid characters are accepted.
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Our Aliphatic Index Calculator is a comprehensive web-based tool designed to analyze the biochemical and physical parameters of your protein sequences. It processes a primary amino acid sequence to compute a wide range of essential physicochemical properties, including the Aliphatic Index, which is a key indicator of protein thermostability. This analysis provides crucial insights that help researchers predict protein structure, function, and stability, facilitating experimental design in fields like protein engineering, purification, and molecular biology.
How to Use
Analyzing your protein sequence is a simple, four-step process:
- Locate the Input Box: Find the text area labeled “Input Protein Sequence.”
- Enter Your Sequence: Paste your protein sequence into the text box using the standard one-letter amino acid codes (e.g., MVLSPADKTN…).
- Analyze: Click the blue “Analyze Sequence” button to initiate the computation. The “Clear All” button can be used to reset the input field.
- Review Results: The tool will automatically calculate and display a detailed report of the protein’s physicochemical properties.
Tip: Before analysis, ensure your input contains only the 20 standard amino acid characters and is free from spaces, numbers, or non-standard symbols to prevent processing errors.
How is the Aliphatic Index Calculated?
The Aliphatic Index of a protein is a critical measure that reflects its thermal stability. It is defined as the relative volume occupied by the aliphatic side chains of specific amino acids: Alanine (Ala), Valine (Val), Isoleucine (Ile), and Leucine (Leu). A higher Aliphatic Index is generally correlated with increased thermostability in globular proteins.
The calculation is based on an empirical formula that assigns weighted values to the mole percent of these amino acids in the sequence:
Aliphatic Index = X(Ala) + a × X(Val) + b × (X(Ile) + X(Leu))
Where:
- a (2.9) and b (3.9) are empirically determined coefficients representing the relative volume of the Val, Ile, and Leu side chains compared to that of Alanine.
- X(Ala), X(Val), X(Ile), and X(Leu) represent the mole percent (mole fraction × 100) of each respective amino acid.
Features and Outputs
This tool provides a comprehensive suite of analyses and outputs for your protein sequence:
- Amino Acid Composition: Provides the absolute count and percentage frequency for each of the 20 standard amino acids.
- Molecular Weight (MW): Calculates the molecular weight of the protein sequence based on the average isotopic masses of the amino acids.
- Theoretical Isoelectric Point (pI): Estimates the pH at which the protein has a net neutral charge, which is crucial for purification and electrophoresis methods.
- Amino Acid Property Groups: Classifies and totals amino acids based on their chemical properties (e.g., Hydrophobic, Polar, Positively Charged, Negatively Charged).
- Atomic Composition: Provides the total count of each type of atom (Carbon, Hydrogen, Nitrogen, Oxygen, Sulfur) that constitutes the protein.
- Extinction Coefficient: Estimates the molar absorption coefficient of the protein at 280 nm, which is useful for determining protein concentration via UV spectroscopy.
- Estimated Half-Life: Offers a prediction of the protein’s stability and lifespan within different biological systems (mammalian, yeast, and E. coli).
- Instability Index: Computes an index to predict the stability of the protein in a test tube. A value below 40 indicates a stable protein.
- Aliphatic Index: Calculates the relative volume of the protein occupied by aliphatic side chains (Alanine, Valine, Isoleucine, and Leucine), which is correlated with thermostability.
- Grand Average of Hydropathicity (GRAVY): A score representing the overall hydrophobicity of the protein. Positive values indicate a hydrophobic nature, while negative values suggest a hydrophilic nature.
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FAQ
References & Suggested Reading
This tool was developed in line with established principles in computational biology 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.
- Ikai, A. (1980). Thermostability and aliphatic index of globular proteins. Journal of Biochemistry, 88(6), 1895–1898. https://doi.org/10.1093/oxfordjournals.jbchem.a133120
- 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
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.