Fluorescent protein controls enzyme activity

November 8, 2012 § Leave a comment

The fluorescent Dronpa domain-enzyme hybrid gives insight into protein activity. DH is a domain that activates Rho-family small GTPases. Image provided by Michael Lin.

These days, we can’t imagine doing molecular biology experiments without green fluorescent protein and other fluorescent tags, using them to visually keep track of our favorite biological molecules. Now, as described in a paper just out in Science, researchers have made one of these fluorescent proteins do more than just work as a tracker. This engineered fluorescent protein can control a protein’s activity.

“I have always been interested in how local and transient protein activities govern complex cell behaviors, such as cytokinesis, cell migration and neuronal differentiation,” says Michael Lin of Stanford University who spearheaded the project. “To understand these processes, it would be a big help to have some way of controlling protein activities tightly in space and time.”

He and his colleagues decided to work with the Dronpa fluorescent protein, a GFP-like molecule that can be easily turned on and off with light beams. The investigators made a molecule in which Dronpa domains that were sensitive to fluorescent light were fused to both ends of an enzyme domain.

In the absence of an external light source, the Dronpa domains associated and caged in the enzyme. They also gave off fluorescent light that could be viewed with an optical microscope.

But when the Dronpa domains were hit with an external pulse of light, the Dronpa domains let go of each other and allowed the enzyme to become activated. The Dronpa domains gave off less light in their dissociated state, indicating that the protein was active and working.

Lin and colleagues tested out their approach with guanine nucleotide exchange factor and protease domains. Lin says using a fluorescent protein to control a protein’s activity could lead to some interesting experiments. “Optical control of protein activities allows us to investigate functions of specific proteins at a level of resolution that otherwise would not be possible. With light control, we could turn on a protein while we observe the cell to understand the time course of signaling events downstream of the protein’s activation,” he says. Also, “we could turn on a protein only in one part of the cell to learn how cell shape can be altered by signal localization.”

Lin and colleagues are now working to extend their approach to other types of fluorescent proteins. Stanford University has filed a patent application for Lin’s approach, which  falls into the realm of optogenetics, a hot area of research where researchers are combining the tools of molecular biology and optics.

Lin is very excited about the potential for controlling protein activity with these engineered fluorescent molecules. He says fluorescent proteins, like GFP, already have revolutionized molecular and cellular biology by acting as tracking units on proteins. Now Lin thinks there is another revolution afoot, where these fluorescent proteins, in combination with pulses of light, will also be capable of controlling protein activities.

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