SDS-PAGE
Say it: es-dee-es-PAYJ
Short for sodium dodecyl sulfate-polyacrylamide gel electrophoresis
SDS-PAGE is a lab technique that separates proteins by size, coating them in a charged detergent and pulling them through a gel with an electric field.
Also: SDS gel electrophoresis, SDS polyacrylamide gel electrophoresis
Definition
What is SDS-PAGE?
SDS-PAGE is the most widely used method for separating proteins according to their size. Samples are heated with sodium dodecyl sulfate (SDS), a negatively charged detergent, usually along with a reducing agent such as beta-mercaptoethanol or dithiothreitol that breaks disulfide bonds. SDS unfolds each polypeptide and coats it with negative charge roughly in proportion to its length, so differences in shape and natural charge are largely erased.
The treated samples are loaded into wells in a polyacrylamide gel, a mesh whose pore size depends on the acrylamide concentration, and an electric field draws the proteins toward the positive electrode. Small proteins slip through the mesh faster than large ones, so the mixture spreads out into bands by mass. A ladder of marker proteins of known size, run in a neighboring lane, lets each band's mass be estimated, and the bands are made visible with Coomassie blue dye or silver stain. The standard version was described by Ulrich Laemmli in 1970.
SDS-PAGE is used to check the purity of a protein preparation, to estimate molecular weight and as the first step of a Western blot. It forms the second dimension of two-dimensional gel electrophoresis, after isoelectric focusing. Because the proteins are denatured, it says nothing about their activity; native gels are used when that matters.
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Terms that go with it
- Gel electrophoresisGel electrophoresis is a lab technique that uses an electric field to pull DNA, RNA or proteins through a gel, separating them by size.
- Western blotA Western blot is a laboratory method that detects a specific protein in a sample by separating proteins by size on a gel and probing them with antibodies.
- Isoelectric focusingIsoelectric focusing is a technique that separates proteins by their isoelectric point, the pH at which a protein carries no net electric charge.
- DenaturationIn biochemistry, denaturation is the unfolding of a protein or nucleic acid by heat, acid or chemicals, which ruins its shape but not its sequence.
- ProteinA protein is a large molecule made of one or more chains of amino acids, folded into a specific shape that determines its job in the body.
- Quaternary structureQuaternary structure is the way two or more folded polypeptide chains, called subunits, fit together to form a single working protein.
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Written for biofideX in plain words, after checking these references:
- Nowakowski et al. (2014), Native SDS-PAGE: High Resolution Electrophoretic Separation of Proteins With Retention of Native Properties Including Bound Metal Ions, Metallomics
- Harper et al., Comparing Complex Protein Samples Using Two-Dimensional Polyacrylamide Gels, Current Protocols in Protein Science
- NCBI MeSH: Electrophoresis, Polyacrylamide Gel
- NHGRI Talking Glossary: Electrophoresis
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