A remarkably stable enzyme known as subtilisin----widely used in laundry detergents----has led to a major advance in purification of proteins of scientific and pharmaceutical interest. This breakthrough makes it easier to rapidly recover highly purified, functional proteins. The method will soon be marketed as the flagship product of a UMBI spin-off company known as Potomac Affinity Proteins, the brainchild of UMBI professor Philip Bryan. Affinity methods are the simplest way to purify a protein: you bind, wash it, and elute it, said Bryan. Recombinant proteins are frequently fused with other proteins which can be used as affinity tags. The tags provide a temporary hook for affinity purification, but ultimately must be removed in an enzymatic step. Tag removal is inefficient and often problematic. What is revolutionary about this method is the integration of tag removal into the purification process. It has all the advantages of other affinity technology, where you bind and wash, but then the purified protein can be released, in a single step, ready to go, in native form, without the tag attached. Affinity purification----which is based on selective binding of a desired substance to a solid support-- is widely used for recovery of purified protein products, including vaccines, pharmaceuticals, diagnostics and reagents for biomedical research. The new method uses a highly modified, patented form of subtilisin known as S189. Subtilisin is a protease----meaning that it breaks bonds on protein chains. S189 has been designed to selectively break one specific bond in a strategic location----and only when it is triggered to do so. As shown in the diagram, the purification system has two basic components: 1) the affinity tag which can be attached to any target protein using standard recombinant DNA techniques and 2) the S189 enzyme which first captures the tagged target protein and then removes the affinity tag, releasing the purified target protein in a single step. In addition to substantial cost savings, the method makes it possible to rapidly purify a variety of different protein targets with a single type of affinity tag. This could become very important when, for example, it is important to rapidly manufacture vaccines for new emergent viral diseases such as influenza, or to respond rapidly to bioterrorism. The S189 chromatography resin and plasmid vectors for cloning the affinity tag onto target proteins will be marketed to the life sciences research community in 2008 through a partner. Potomac Affinity will focus on further engineering of proteases for new applications in protein analysis, detection and therapeutics. | 
