Two-dimensional gel electrophoresis of membrane proteins

A high-resolution method for two-dimensional separation of membrane proteins is described. It involves a nondiscriminating solubilization of a membrane preparation with sodium dodecyl sulfate, followed by electrophoresis in the first dimension according to charge (by isoelectric focusing). The electrophoresis in the second dimension is in the presence of sodium dodecyl sulfate, thus separating proteins on the basis of molecular weight. Electrophoresis in the first dimension is either on a thin slab gel, or on a small-diameter tube; electrophoresis in the second dimension is on a thin slab gel. Up to 100 mug of protein can be analyzed. The two-dimensional system is a modification of the one recently described by O'Farrell (1975). About 150 different proteins can be visualized in Escherichia coli or Salmonella typhimurim cell envelopes; examples of differences between mutant and wild-type strains are presented. The method is applicable also to membrane preparations from other sources: a two-dimensional separation of plasma membrane proteins from HeLa cells is presented.