Dr. Vanessa Ruta Explores the Evolution of the Insect Olfactory System

Insects have unique diets: butterflies bounce from flower to flower in search of nectar, aphids suck the sap out of leaves, and mosquitos infiltrate outdoor gatherings to prey on those who forgot bug spray. Each uses its finely tuned sense of smell to seek out its next meal, but since each is looking for a different food, this system must be customized to help find a specific target.

A new study from NYSCF – Robertson Neuroscience Investigator and The Rockefeller University Gabrielle H. Reem and Herbert J. Kayden Associate Professor of Biochemistry, Biophysics, Chemical Biology, and Structural Biology Vanessa Ruta, PhD, explores how the insect olfactory system evolved to allow different insects to find the food they’re looking for.

The way insects smell is dependent on the activity of their odorant receptors. There are many different types of odorant receptors that respond to many different smells, but they all function in the same way. Each is made of an ion channel that opens up when the insect encounters its target odor, allowing charged particles to flow through.

“Insect odorant receptors are very likely the largest family of ion channels in nature, and they’re incredibly diverse,” says Dr. Ruta in a press release issued by The Rockefeller University. “So we were faced with a fundamental mystery: How do you get millions of variants of a channel that are so different but that all do the same thing?”

To find out, the team focused on a certain channel subunit called Orco. In the olfactory system, an ion channel consists of one Orco protein and a bunch of receptor proteins that vary from species to species.

The team used a method called cryoelectron microscopy to study the structure of a channel made of all Orco proteins. They found that this channel, called an Orco homomer, consists of four subunits bound at one point — the “anchor domain”— and a central pore that the ions flow through.

The structure of the Orco homomer helps explain why insect olfactory receptors evolved to become so diverse. Since each of the subunits are placed relatively far from the others, they can act more independently than if they were packed together. The anchor domain helps the receptor carry out its key function, but the subunits are free to evolve over time.

The team again noticed this pattern when analyzing the odorant receptors of four different insect species. While their proteins varied, each receptor had similar pores and anchor domains. The researchers believe that the receptors are structured this way so that even as the subunits evolve over time, the channel still functions consistently.

In addition to helping us better understand evolutionary mechanisms, this study has implications for human disease. Malaria, the Zika virus, and dengue fever can all be transmitted through mosquito bites, so if we can block a mosquito’s ability to sniff out humans by interfering with its olfactory receptors, we can possibly prevent the spread of these illnesses.

For more information, check out the full study in Nature.