Fluorescent proteins are used widely in biological research to monitor molecules and events in living cells, but now researchers at Stanford University have found that one of those proteins—called Dronpa—has another valuable application: it can be used to control the function of other proteins via light.
In a paper published recently in Science (1), Michael Lin and colleagues found that Dronpa fluoresces when two or more of its domains bind; a single Dronpa domain cannot fluoresce on its own. Light of different wavelengths induces conformational changes in the protein’s structure. So, under cyan light, most Dronpa protein domains are separated and don't fluoresce. Meanwhile, violet light induces a structural change in the protein that allows these domains to bind and fluoresce.
The researchers wanted to see if it was possible to take advantage of this light-induced domain pairing to control another protein's activity. They attached one of the reactive Dronpa domains to one end of a protein called intersectin, which controls the formation of actin filaments involved in cell movement. Then, they attached the other domain to the other end of intersectin.
As a result, the two Dronpa molecules bound to each other under violet light, creating a caged protein that couldn't function normally and interrupting the production of actin. When cyan light shone on the protein, the Dronpa domains released from each other, allowing normal intersectin function to resume. In addition, Dronpa acts as a reporter of its own activities in protein control because of its fluorescence.
This is the first technique developed in which a single proteins functions as both a control and reporter of protein activity, said Lin. He and his colleagues call these controllable biomolecules fluorescent light-inducible proteins (FLIPs).
Using this technique, researchers should be able to control just about any protein they want to study, according to Lin. While other light-inducible proteins require very specific molecular linkages that could take years of screening to achieve, Dronpa has simple linkages at the ends of proteins, which will likely make it easy to attach to other proteins.
"We wanted to make a way that was more generalizable—that you could just tweak a few attachments and make a light-inducible protein," he said.
1. Zhou, X. X., H. K. Chung, A. J. Lam, and M. Z. Lin. 2012. Optical control of protein activity by fluorescent protein domains. Science 338:810-814.