When the VA pheromone contacts a tiny hair on a fly's antenna, it binds with the LUSH protein. Once bound, the LUSH protein changes its shape so it can fit into a receptor on the surface of a specific olfactory neuron inside the hair, which sends the appropriate behavioral signal to the bug.
"Without LUSH as a bridge, this pheromone can't get its signal to the neuron and the fly doesn't behave normally," Dr. Smith said. His research group reinstated the correct behavior in the mutant flies by injecting them with the missing lush gene.
In the absence of the pheromone, the researchers found that LUSH still binds to the olfactory neuron, sparking the neuron to fire a small electrical signal called "spontaneous activity." With the pheromone present, and bound to LUSH, the neuron exhibits a large burst of normal electrical activity. In mutants lacking LUSH, however, they found a 400-fold reduction in spontaneous activity, indicating that LUSH is necessary for the neuron to function properly.
"This reduction in spontaneous activity was a surprising finding," Dr. Smith said. "Our results indicate that LUSH, and not the pheromone, is what directly activates the chemosensory neurons. It is likely that OBPs in other insects also work this way, although the pheromones are different in different species. We think that OBPs might be new targets for insect control and repellents." Other studies have also linked OBPs to insect behavior. A 2002 fire ant study suggested a role for OBPs in worker ants' ability to recognize queens and regulate the number of queens in a colony.