How to make a molecular switch

Researchers at Johns Hopkins University joined two proteins in such a way that one member controls the activity of the other. Similarly coupled proteins may be used to produce specialized molecules that deliver lethal drugs only to cancerous cells or to set off a warning signal when biological warfare agents are present.

"We've taken two proteins that normally have nothing to do with one another, spliced them together genetically, and created a fusion protein in which the two components now 'talk' to each other," says Marc Ostermeier, assistant professor in the Dept. of Chemical and Biomolecular Engineering. "More importantly, we've shown that one of these partners is able to modulate or control the activity of the other. This could lead to exciting practical applications in medical treatment and biosensing," he adds.

Researchers created the switch by first placing beta-lactamase genes inside genes for maltose-binding protein. They snipped the maltose-binding genes as though they were tiny strips of paper.

A second enzyme was used to reattach the severed strips to each side of a beta-lactamase gene, producing a single gene strip. The random cut-and-paste process created combined genes that produced new proteins with different qualities.

To test the new fusion proteins for molecular-switch behavior, researchers looked for E. coli that thrived in maltose. Mixing in an antibiotic revealed proteins in which the beta-lactamase remained active enough to react against the antibiotic. Researchers discovered two fusion proteins in which the presence of maltose actually caused the beta-lactamase partner to step up its attack on the antibiotic. "One part of this coupled protein sent a signal, telling the other part to change its behavior," explains Ostermeier. How is this useful? "One part of a fusion protein might react to the presence of a biological-warfare agent, signaling its partner to set off a bright green fluorescent glow to alert soldiers," he says.