The tool -- a special fluorescent protein -- probes the activity of cyclic AMP in living cells and represents biology's growing application of a fluorescent phenomenon to study the molecular changes that reveal cells' inner workings.
Much like a child might pass along a visitor's request to a grown-up, cyclic AMP carries messages from hormones or other molecules "knocking" at the cell's door to proteins inside the cell. But because cyclic AMP uses just a handful of proteins to pass on many messages, scientists have had a hard time figuring out how it can trigger the right cellular response to each one.
"Scientists suspected that timing and location of cyclic AMP activity was important, but there was no easy way to study cyclic AMP inside cells in real time and in real space," says Jin Zhang, Ph.D., senior author of the study and an assistant professor of pharmacology and molecular sciences and of neuroscience in Johns Hopkins' Institute for Basic Biomedical Sciences. "This new fluorescent protein can be directed to the nucleus or to other parts of the cell, so we can now follow cyclic AMP activity in real time and space."
The new fluorescent protein takes advantage of the fact that fluorescent molecules can "talk" to one another when they are close together, affecting the color of light emitted -- a phenomenon called fluorescent resonance energy transfer (FRET). If the distance between the fluorescent molecules changes, the color of light emitted may change as well.