Smell

P.I.: Jérôme Golebiowski

Martine Adrian-Scotto, Serge Antonczak, Sebastien Fiorucci.

Despite important efforts that have been made for understanding the molecular basis of olfactory perception, many questions remain unanswered. We use computational approaches to gain informations on the mechanistic events underlying the perception of odors. Molecular dynamics simulations are for example preformed to understand the atomic-level properties of Odorant Binding Proteins and Olfactory Receptors.

Chemical senses at the molecular level

  • From a molecule to an odour (movie, ~8 minutes).

 

 

 

Chemoreception is the aptitude of living organisms to identify chemical compounds in their environment and to evaluate their concentration. Olfaction is initiated by a molecular interaction of chemicals called odorants with olfactory neurons located in the epithelium of the nasal cavity. see our 3D movie, from a molecule to an odour in a separate page.

Glomerules belong to the part of the brain that collects informations brought by Olfactory Neuron activation. The neuron cilia project down out of the olfactory epithelium into an aqueous layer, preventing them from drying out: the olfactory mucus (yellow waves).

On the surface of these neurons, the signal is transmitted when an olfactory receptor is activated by an odorant.

Click on the bottom of the small box at the left (ooo), you’ll see how an odorant mixture signal is decomposed by the neurons and their correponding glomerules.

The small circles (the odorants) generally activate a given type of neuron, but the specificity is low, so that a “green” odorant can activate a “blue” neuron. You can see it by clicking on the “green-blue” mixture (oo), or only the pure green odorants(o).

This lack of selectivity endows the system a spectacular discriminatory power, able to perceive many thousands of odors.

  • Olfactory Receptors

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On the surface of the olfactory neurons, the activation of Olfactory Receptors, a class of protein belonging to the GPCR family and dedicated to transmit the signals to the brain, originates odour perception. Humans share ~ 1000 types of ORs, of which ~ 350 are considered to be functional. The biological method of chemical recognition is far from the simple “lock and key” analogy, since a single OR can be activated by multiple odorants, and a single odorant can activate several ORs.

  • Odorant Binding Proteins

obpPrior to their interaction with ORs, odorants are associated with Odorant Binding Proteins (OBPs) present in the olfactory mucus. OBPs belong to a class of carrier proteins present in physiological fluids. They are thought to contribute actively to the transport of the odorant from the inhaled air stream through the mucus to the cilia of the olfactory neurons. The role of these OBPs stills need to be explored in details.