GENETIC-ENGINEERING TO ENHANCE THE SELECTIVITY OF PROTEIN SEPARATIONS

The ability to recover and purify natural and recombinant proteins, an d the costs of doing so remain a major task in introducing the potenti al products of biotechnology. The bases for separation range from spec ific binding onto tailored reagents to solubility and partitioning beh avior governed by a mixed bag of size, charge, and hydrophobicity. In most cases, a combination of methods is used in sequence, and improvem ents in the selectivity at an early stage can enhance the effectivenes s of subsequent (and usually more costly) steps. Genetic engineering p rovides a means of improving the selectivity within the context of exi sting separation methods. By this strategy, improvements in selectivit y are sought by bestowing a distinctive property on the protein of int erest. The primary sequence of amino acids is altered, such that the p rotein can be selectively removed from other components of the multico mponent mixture in which such products are commonly found. In this art icle, the range of these ''distinctive properties'' and their pairing with various separation methods will be reviewed. Specific examples fr om our work, in which a distinctive charge is provided via a polypepti de ''purification'' fusion tail, will be discussed. Separation methods we have used with these fusion proteins are precipitation, two-phase aqueous extraction, reversed micellar extraction, and ion exchange usi ng both resins and membranes.