Two-dimensional gel electrophoresis

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Coomassie-stained 2D gel

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Spot cutting and pipetting robot used in 2D gel electrophoresis

Original dual-channel 2D gel image

Warped dual-channel 2D gel image

Two-dimensional gel electrophoresis (2-DE) is a powerful analytical technique used to separate proteins based on two distinct properties: isoelectric point and molecular weight. This method is widely used in proteomics to analyze complex protein mixtures extracted from cells, tissues, or other biological samples.

Methodology

The process of two-dimensional gel electrophoresis involves two main steps:

First Dimension: Isoelectric Focusing

In the first dimension, proteins are separated by isoelectric focusing (IEF). This technique separates proteins based on their isoelectric point (pI), the pH at which a particular protein carries no net charge. Proteins are applied to a gel strip containing a pH gradient, and an electric field is applied. Proteins migrate through the gel until they reach a point where the pH equals their pI, at which point they stop moving.

Second Dimension: SDS-PAGE

After isoelectric focusing, the gel strip is placed on top of a second gel, typically a sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) gel. In this dimension, proteins are separated based on their molecular weight. SDS, a detergent, denatures proteins and gives them a uniform negative charge, allowing them to be separated by size when an electric field is applied.

Applications

Two-dimensional gel electrophoresis is used in various applications, including:

• Protein Identification: By comparing the pattern of protein spots on a 2D gel with known standards, researchers can identify proteins present in a sample.
• Differential Expression Analysis: By comparing 2D gels from different samples, such as healthy vs. diseased tissues, researchers can identify proteins that are differentially expressed.
• Post-translational Modifications: 2-DE can be used to detect changes in protein isoforms due to post-translational modifications.

Advantages and Limitations

Two-dimensional gel electrophoresis offers high resolution and the ability to separate thousands of proteins in a single run. However, it has limitations, including difficulty in resolving very large or very small proteins, membrane proteins, and proteins with extreme pI values. Additionally, the technique can be labor-intensive and requires significant expertise.

Related pages

• Electrophoresis
• Proteomics
• Isoelectric focusing
• SDS-PAGE