Study reveals how smell receptors work
Aug 2021, phys.org
Big smell news - for the first time ever, using cryo-electron microscopy, we can see an olfactory receptor in action. And as expected, it doesn't work like any other receptor.
Odorant receptors are known for their 'promiscuous chemical sensitivity;' that's a scientific term, by the way. It means that any one receptor might be sensitive to hundreds of molecules, so it's been really hard to figure out what makes any particular molecule match with a receptor.
They looked at the jumping bristletail (surprise - not the fruit fly) because it has only five types of receptors, and because one of those receptors (OR5) is really broad, responding to 60% of the smell molecules they presented to it (promiscuous).
So they look at this receptor in its default state, and then again as they expose it to smell molecules (either eugenol or DEET).
And? Its ion channel pore dilates. That's it. Both of the competing theories about how smells work were wrong. It turns out they work via nonspecific chemical interactions -- they are not recognizing a specific chemical characteristic, but something more general about the molecule itself.
And there you have it! Olfaction is still one of the strangest senses we have.
Don't forget to thank cryo-electron microscopy, and the hundreds of scientists who have been trying to figure this out over the past hundred years.
via Rockefeller University: del Mármol, J., Yedlin, M.A. & Ruta, V. The structural basis of odorant recognition in insect olfactory receptors. Nature (2021). https://doi.org/10.1038/s41586-021-03794-8