Scientists may have solved the mystery behind how we smell
Scientists from the University of California San Francisco (UCSF) have, for the first time, created a precise, molecular-level, 3D structure of how an odor molecule activates an odorant receptor in humans. The research focuses on an olfactory receptor, called OR51E2, and shows how it 'recognizes' the smell of cheese through certain molecular interactions that turn on the receptor.
Why does this story matter?
The odor receptors in our nose help us distinguish between the different kinds of smells-pleasant, pungent, and so on. But so far, little has been known about how these receptors detect molecules and convert them into scents. Now, with the first-ever 3D picture of the structure of our odor receptors, we might be closer than ever to solving the mystery behind how we smell.
Humans can distinguish over one trillion scents, claims a study
Odorant receptors—proteins present on the surface of olfactory cells that bind odor molecules—constitute half of the largest, most diverse type of receptors in humans. The human genome contains genes encoding 400 olfactory receptors, reports Nature. In the 1920s, researchers predicted the human nose could differentiate about 10,000 smells, but a 2014 study suggests that we can distinguish over one trillion scents.
A single odorant can activate multiple receptors
Each olfactory receptor can only interact with a specific set of odorants while a single odorant can activate multiple receptors. This can be compared to "hitting a chord on a piano", said Aashish Manglik, co-author of the study. "Instead of hitting a single note, it's a combination of keys that are hit that gives rise to the perception of a distinct odor."
The OR51E2 receptor has functions beyond odorant recognition
It is not well understood exactly how olfactory receptors pick up specific odorants and translate them to different smells in the brain. Further, producing mammalian olfactory-receptor proteins in the laboratory is challenging. Hence, the team turned to the OR51E2 receptor. It has functions beyond odorant recognition and along with olfactory neurons, it is also found in gut, kidney, and prostate tissues.
The OR51E2 receptor interacts with two molecules, acetate and propionate
The OR51E2 receptor interacts with two odorant molecules. One is acetate, which smells like vinegar and the other is propionate, which has a cheesy odor. Researchers found that the propionate molecule binds to OR51E2 through specific ionic and hydrogen bonds creating what's called a 'binding pocket' in the receptor. This interaction changes the shape of OR51E2, which causes the receptor to get activated.
"For us, this is just the beginning"
"We now have our first toehold, the first glimpse of how the molecules of smell bind to our odorant receptors," said Manglik. "For us, this is just the beginning." The paper has been published in the journal Nature.
