Two-Dimensional Electrophoresis: The State of the Art and Future Directions

Abstract

Two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) is the only method currently available which is capable of simultaneously separating thousands of proteins. Thus 2-D PAGE is the heart of proteome technology. The first dimension of 2-D PAGE is isoelectric focusing (IEF), during which proteins are separated in a pH gradient until they reach a stationary position where their net charge is zero. The pH at which a protein has zero net charge is called its isoelectric point (pI). In the second dimension the proteins separated by IEF are separated orthogonally by electrophoresis in the presence of sodium dodecyl sulphate (SDSPAGE). The surfactant SDS binds to proteins, overriding their intrinsic charge, such that they all have the same charge density and free solution electrophoretic mobility. When the SDS-coated proteins migrate in a sieving polyacrylamide gel they separate based on their molecular mass. The high resolution of 2-D PAGE results from the first and second dimension separations being based on independent protein parameters.