Washington, April 14 : The discovery that insects have adopted a strategy to detect odors that is radically different from those of other organisms, may challenge an important theory of evolution.
The new theory was put forward by researchers at the Rockefeller University in the US and the University of Tokyo in Japan.
Since 1991, researchers assumed that all vertebrates and invertebrates smell odors by using a complicated biological apparatus.
In the case of an insect's ability to smell, researchers believed that when molecules wafting in the air travel up the insect's nose, they latch onto a large protein (called a G-protein coupled odorant receptor) on the surface of the cell and set off a chain of similarly elaborate steps to open a molecular gate nearby, signaling the brain that an odor is present.
According to study co-author Leslie Vosshall, head of the Laboratory of Neurogenetics and Behavior at Rockefeller University, "It's that way in the nematode, it's that way in mammals, it's that way in every known vertebrate. So, it's actually unreasonable to think that insects use a different strategy to detect odors."
"But here, we show that insects have gotten rid of all this stuff in the middle and activate the 'gate' directly," he added.
The gate, a doughnut-shaped protein called an ion channel, provides a safe pathway for ions to flow into a cell. When molecules bind to the odor-sensitive ion channel, the protein changes its shape much like a gate or door changes its conformation as it is opened and closed.
Opened, it allows millions of ions to surge into the cell. Closed, it prohibits the activity of the ions from sending a signal to the brain that an odor is present.
At the University of Tokyo, Vosshall's colleague Kazushige Touhara and his lab members puffed molecules onto cells engineered to make insect olfactory receptors.
They then measured how long it took for the ion channel to open and recorded their electrical movement as they surged inside the cell via the channel.
"The rush of electrical activity occurred too fast for a series of steps to be involved," said Vosshall. "In addition, poisoning several proteins involved in the G-protein pathway didn't affect the ions or the ion channel, suggesting that G-protein signaling isn't primarily involved in insect smell," he added.
"Experiment after experiment, the most consistent interpretation is that these are ion channels directly gated by odors," said Vosshall.