Of the human senses, the sense of smell is the least understood. Now, scientists at the University of Illinois at Urbana-Champaign have sniffed out potential clues to how olfactory receptors in the nose detect odors. Those clues may also explain why dietary zinc deficiencies lead to a loss of smell.

Olfactory receptors are proteins that bridge through the cell membrane. Kenneth S. Suslick and his colleagues - Zaida A. Luthey-Schulten and Jiangyun Wang - investigated the possibility that olfactory receptors are metalloproteins (proteins that contain a metal ion as part of their structure) and have found that the structure of the protein changes dramatically when a zinc or copper ion binds to it. They propose that the olfactory response to an odorant involves this change in structure that pushes and pulls part of the olfactory receptor protein into and out of the cell in a 'shuttlecock' motion. This back-and-forth motion passes information through the cell membrane.

The average human nose can detect nearly 10,000 distinct scents, a feat that requires about 1,000 olfactory genes, or roughly 3 percent of the human genome. Only recently have the genes responsible for smell been identified. "When we searched the genome data, we found an identical site in more than 75 percent of the olfactory receptors that looks like it can bind to metal ions very strongly," Suslick said. The structure of these receptors is thought to be a protein that weaves in and out of the cell membrane seven times. Between the fourth and fifth helices, the scientists found an uncommonly long loop that they suspected contained the binding site for a metal ion. >from *Metal Ions May Play Big Role In How We Sense Smells*, february 24, 2003

related context
> how the nose knows a rose-or a mate (odors and pheromones). february 13, 2003
> insects' sense of smell: key step uncovered. january 10, 2002
> how mammals distinguish different odors. march 5, 1999

imago
> metalloproteins sprinkler