Drugs based on engineered proteins represent a new frontier for pharmaceutical makers. Even after they discover a protein that may form the basis of the next wonder drug, however, they have to confront a long-standing problem: how to produce large quantities of the protein in a highly pure state. Now, a multi-institutional research team including a biochemist at the National Institute of Standards and Technology (NIST) may have found a new solution in an enzymatic "food processor" they can activate at will.
The team has found an efficient method of harvesting purified protein molecules by altering an enzyme that soil bacteria use to break down their food. In its natural form, this enzyme would be of little use to drug developers, but the team has modified it so that it can be activated at the desired moment. By creating essentially an "on-switch" for the enzyme's activity, the team has found a way to separate a single, desired protein from the mixture of thousands generated by a living cell, which remains biotechnology's natural protein factory of choice.
Bacteria use the enzyme, called subtilisin, as a sort of food processor: After producing it internally, they release the enzyme into the soil, where it uses a minuscule "blade" to chop up proteins into digestible pieces. Because it could damage the bacterium's interior, the blade has a protective sheath that only comes off once the enzyme has exited the cell.
"The enzyme and sheath are strongly attracted to each other. The enzyme's first act is to cut the sheath away," says NIST's Travis Gallagher. "The method takes advantage of their attraction in order to isolate the protein we want."