Affinity chromatography theoretically does just that—a ligand that specifically interacts with the target protein is immobilized on a chromatography matrix; the target protein binds to the column, and unwanted proteins are eluted. In some cases, the affinity ligand is an antibody against the protein of interest; in others, the target protein is expressed from a plasmid that encodes for an "affinity tag" specific to a particular ligand.
This article discusses some of the affinity fusion systems available for recombinant proteins expressed in E. coli. A list of companies offering complete affinity fusion protein-purification systems (vectors and resins) is shown in the accompanying table.
Although the GST tag is more difficult to use than its popular competitor, the polyhistidine tag, many protein chemists prefer it because its use has been so well documented. "The six-His tag has become very popular, and a lot of scientists choose it, but ... a lot ...
