Understanding sense of smell: Scientists create 3D image of odour molecule

We generally know about particles. Everything is made up of atoms and molecules. We all know this. But when is comes to sense of smell, the molecular level understanding is something that's not common knowledge. What is a smell? How do we perceive it? These are some of the questions scientists have been working upon for decades. And there has now been a breakthrough finally.

Scientists have created the first molecular-level, 3D picture of how an odour molecule activates a human odorant receptor, a crucial step towards deciphering the sense of smell.

This will help a longstanding impasse in our understanding of olfaction (sense of smell). The 3D picture of the odour molecule has implications for fragrances, food science and beyond.

The 3D model has been created by scientists at University of California San Francisco (UCSF). This is sure to reignite interest in the sense of smell.

The findings have been published in the journal Nature, reported Press Trust of India.

Odorant receptors, proteins that bind odour molecules on the surface of olfactory cells, make up half of the largest, most diverse family of receptors in our bodies. A deeper understanding of them paves the way for new insights about a range of biological processes.

Smell involves about 400 unique receptors.

Each of the hundreds of thousands of scents we can detect is made of a mixture of different odour molecules. Each type of molecule may be detected by an array of receptors, creating a puzzle for the brain to solve each time the nose catches a whiff of something new.

"It's like hitting keys on a piano to produce a chord," said Hiroaki Matsunami, professor at Duke University and a close collaborator of Aashish Manglik, associate professor, UCSF.

Matsunami's work over the past two decades has focused on decoding the sense of smell.

"Seeing how an odorant receptor binds an odorant explains how this works at a fundamental level," said Matsunami.

We haven't been able to map olfaction, because without a picture, said Manglik, we didn't know how odour molecules would react with their corresponding odour receptors.

To create the 3D picture, the study said, Manglik's lab used a type of imaging called cryo-electron microscopy (cryo-EM), that allows researchers to see atomic structure and study the molecular shapes of proteins.

But before Manglik's team could visualise the odorant receptor binding an odorant, they first needed to purify a sufficient quantity of the receptor protein.

Odorant receptors are notoriously challenging, some say impossible, to make in the lab for such purposes.

The Manglik and Matsunami teams looked for an odorant receptor that was abundant in both the body and the nose, thinking it might be easier to make artificially, and one that also could detect water-soluble odorants, according to the study.

They settled on a receptor called OR51E2, which is known to respond to propionate, a molecule that contributes to the pungent smell of Swiss cheese.

(With inputs from agencies)

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