How you sense a smell—as pleasant or offensive—may be decided by a difference at the smallest level of DNA—one amino acid on one gene, researchers say.
There are about 400 genes coding for the receptors in our noses, and according to the 1000 Genomes Project, there are more than 900,000 variations of those genes. These receptors control the sensors that determine how we smell odors. A given odor will activate a suite of receptors in the nose, creating a specific signal for the brain.
But the receptors don’t work the same for all of us, says Hiroaki Matsunami, associate professor of molecular genetics and microbiology at the Duke University School of Medicine. In fact, when comparing the receptors in any two people, they should be about 30 percent different.
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While researchers had earlier identified the genes that encode for odor receptors, it has been a mystery how the receptors are activated. To determine what turns the receptors on, researchers cloned more than 500 receptors each from 20 people that had slight variations of only one or two amino acids and systematically exposed them to odor molecules that might excite the receptors.
By exposing each receptor to a very small concentration—1, 10, or 100 micromoles—of 73 odorants, such as vanillin or guaiacol, the group was able to identify 27 receptors that had a significant response to at least one odorant.
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