In their hunt for genes and proteins that explain how animals discern bitter from sweet, a team of Johns Hopkins researchers began by testing whether mutant fruit flies prefer eating sugar over sugar laced with caffeine. Using a simple behavioral test, the researchers discovered that a single protein missing from the fly-equivalent of our taste buds caused them to ignore caffeine's taste and consume the caffeine as if it were not there.
"No, you won't see jittery Drosophila flitting past your bananas to slurp your morning java anytime soon," says Craig Montell, Ph.D., a professor of biological chemistry in the Institute of Basic Biomedical Sciences at Hopkins. "The bottom line is that our mutant flies willingly drink caffeine-laced liquids and foods because they can't taste its bitterness -- their taste receptor cells don't detect it."
The Hopkins flies, genetically mutated to lack a certain taste receptor protein, have been the focus of studies to sort out how animals taste and why we like the taste of some things but are turned off by the taste of others.
By color-coding sweet and bitter substances eaten by fruit flies and examining the coloring that shows up in their translucent bellies, the Hopkins team hoped to learn whether flies missing a specific "taste-receptor" protein changed their taste preferences.
"Normally," Montell explains, "when given the choice between sweet and bitter substances, flies avoid caffeine and other bitter-tasting chemicals. But flies missing this particular taste-receptor protein, called Gr66a, consume caffeine because their taste-receptor cells don't fire in response to it."
The discovery, which is the first ever example of a protein required for both caffeine tasting and caffeine-induced behavior, will be published Sept. 19 in Current Biology.
For the study, Montell and his colleagues kept 50 fruit flies away from food overnight and for breakfast gave the starved flies 90 m
Contact: Audrey Huang
Johns Hopkins Medical Institutions