seperation

Two-dimensional Protein Electrophoresis (2DE)

The central tool for displaying the proteome is two-dimensional gel electrophoresis. Proteins areseparated on the basis of charge in the first dimension and molecular mass in the second. Several improvements have been made to this method in the past few years, particularly in the first-dimension separation.

The sample (eg, tissue, serum) is solubilised, and the proteins are denatured into their polypeptide subunits. This mixture is then separated by isoelectric focusing; on the application of a current, the charged polypeptide subunits migrate in a polyacrylamide gel strip that contains an immobilised pH gradient until they reach the pH at which their overall charge is neutral (isoelectric point or pI), hence producing a gel strip containing discrete protein bands along its length. This gel strip is then applied to the edge of a rectangular slab polyacrylamide gel containing sodium dodecyl sulphate, and the focused polypeptides migrate in an electric current into the second gel and are separated on the basis of molecular size.

Typically 1000–3000 interpretation of their expression takes into account their dynamics in specific biological contexts. The expression or function of proteins is modulated at many points from transcription to post-translation , which generally cannot be predicted from analysis of nucleic acids alone. There is poor correlation between the abundance of mRNA transcribed from the DNA and the respective proteins translated from that mRNA, and the proteins per gel can be visualised, for example by staining with silver. Complementary approaches such as immunoblotting allow greater sensitivity for specific molecules. Multiple forms of individual proteins can be readily visualised , and the particular subset of proteins examined from the proteome is determined by factors such as initial choice of sample solubilisation conditions and pH range of the gel strip used for the first dimension.