An analysis of the draft human genome reveals that when it comes to olfaction, a sense of smell is nothing to be sniffed at, with every nose containing an estimated 347 receptor candidates.
Dogs are well known for their highly sensitive sense of smell, but humans too can sniff out thousands of different odors. The trick is to have a family of odor receptors located on the surface of cells lining the nose with each cell expressing just one type of receptor.
This means that a particular smell, gorgonzola cheese, for instance, is detected by activation of a particular combination of receptors, producing a message that the brain interprets as the smell of sweaty feet, sorry, as that delightfully aromatic cheese.
Now, Sergey Zozulya and colleagues from the California-based biotechnology company Senomyx have found that human odorant receptor genes are clustered on particular chromosomes, with the largest group of 155 located in a few clusters on chromosome 11. The team suggests that the presence of the clusters simply reflects duplications of ancestral genes throughout evolution. The team also revealed many pseudogenes, which may have had a use at one time but have become vestigial in people.
Zozulya and his colleagues mined the human genome databases looking for nuggets of conserved DNA motifs. But, as they point out, there may be a few other family members that will be uncovered as the finishing touches are put to the human genome over the next year or two. “We’re fairly confident that we are missing only a small number of receptors (5% or so of the complete set),” Zozulya told Reactive Reports. Interestingly, more than half of all human olfactory receptor genes are dead (pseudogenes) in humans in contrast to the almost completely intact repertoire in animals, such as rodents.
Our sense of smell is at the front line in investigating our chemical environment, whether it is sniffing out the best smelly cheese or making sure the milk has not soured before pouring it over one’s cornflakes. A better understanding of how the receptors distinguish between different smells and why some people can smell certain odors that others cannot, will ultimately lead to new, improved perfumes and flavorings. Senomyx is using recent advances in receptor biology, combinatorial chemistry, high-throughput screening and bioinformatics to quickly discover new and improved proprietary molecules.
Zozulya, S., Echeverri, F., & Nguyen, T. (2001). The human olfactory receptor repertoire Genome Biology, 2 (6) DOI: 10.1186/gb-2001-2-6-research0018