Most animals consider smell to be the most important sense. It helps them find food, avoid danger, attract mates, and it rules their behavior.Bob Datta, a Harvard Medical School neurobiologist, stated that understanding how biological creatures interact with chemistry is fundamental to understanding who we are as well as how we navigate the universe.Original story reprinted by permission of Quanta Magazine. This independent publication published by the Simons Foundation has an editorial policy that allows for the reproduction of this article. It covers research developments in mathematics, the physical and the life sciences and aims to increase public understanding.Olfaction is one of the most complex senses. This is partly because it has to deal with so many different inputs. A single odor, such as the smell of coffee, wet grass after a storm, or shampoo, is often actually a mix of hundreds of chemicals. The limited number of receptors in an animal's olfactory sensory neurons must recognize many compounds for it to distinguish between them. Each receptor must be capable of responding to a variety of odor molecules, even if they are not related.This flexibility is in contradiction to the lock-and-key model that governs how selective chemical interactions tends to work. Annika Barber, Rutgers University molecular biologist, stated that this is what she learned about ligand receptor interactions in high school biology. It must fit exactly in the site. Then it alters [proteins' atomic arrangement]. And then it works.New work is making a significant and highly anticipated breakthrough in understanding the early stages of the olfactory system. A team of scientists from Rockefeller University, New York published a preprint online earlier this year that showed the first molecular view a olfactory receptor binding to an odor molecule. This has been a goal in the field since the discovery of olfactory receptors 30 years ago. Richard Benton, a biologist from the University of Lausanne, Switzerland, was not involved in this new study.Datta stated that it was unquestionably a landmark paper. Even though we have had long-term access to receptors, as molecules, nobody has ever seen what it looks like when an aroma binds to a receptor.This study confirms that animals can distinguish between astronomical amounts of smells. The study also sheds light upon key principles of receptor activity, which could have profound implications for the evolution of chemical perceptual abilities, our understanding of other neurological processes, and practical applications such as the development of targeted medicines and insect repellents.There are many theories that explain how olfactory nerves work. Scientists have suggested that receptors only respond to one feature of odor molecules (such as size or shape) and the brain may then recognize an odor using a combination of these inputs. Others suggested that each receptor could have multiple binding sites which allow different types of compounds to dock. To determine which idea was correct, researchers needed to examine the receptor's actual structure.The Rockefeller team looked at receptor interactions in jumping bristletail, an ancient ground-dwelling insect with a simple olfactory system.Olfactory receptors in insects are ion-channels that activate when an odor molecules binds to them. These ion channels are the most diverse and complex family of ion channel in nature. There are millions of variations across all species of insects. They must balance generality and specificity. This means they have to be flexible enough to recognize a wide range of odors, while still being able to identify the most important. These odors can vary greatly from one species to another.
