Eerie and distinctive, the smell of a dead body comes mainly from small molecules known as diamines, products of degradation of biological tissues. A team of computational biologists at the Autonomous University of Barcelona (UAB) announced that they had revealed the biochemical mechanism behind humans' ability to sense carcasses, which could innovate the diagnosis for patients with mood disorder.
In the mid-19th century, French poet Charles Baudelaire famously expressed his curiosity of morbidity by writing about a decomposing corpse in his work titled “a carcass”. On top of terrifying visual cues, dead bodies give off a sickly-sweet odor that’s immediately recognizable and hard to forget.
The two best-characterized components in the “dead smell” are cadaverine and putrescine. First discovered in 1885 by German physician Ludwig Brieger, they are small molecules produced by the breakdown of the amino acids lysine and methionine, respectively. And several years later the receptor for cadaverine was identified in zebrafish. In recent years, with the advancement of forensic science, the smell of death has become an increasingly important topic due to its potentials as a tool of criminal investigation.
Related: scientists search for death’s aroma
The ability to sense foul-smelling death-associated compounds is evolutionarily crucial for the survival of many species. Previous research has traced human’s ability to sense the "dead smell" to a group of receptors localized in the olfactory epithelium, known as the seven-helix trace amine-associated receptors (TAARs),
TAARs are G protein-coupled receptors (GPCRs), the group of proteins that play an essential role in signal transduction pathways in eukaryotes. In human physiology, GPCRs are responsible for smell, vision, taste and even the regulation of behavior and mood. They also constitute a major drug target—over one-third of current medications targets GPCRs. American biochemists Brian Kobilka and Robert Lefkowitz were given the 2012 Chemistry Nobel for their groundbreaking discovery of how G protein-coupled receptors function.
The Spanish researchers used computational strategies to characterize the binding between cadaverine and putrescine with the TAAR6 and TAAR8 human receptors, which are among the least understood TAARs. Their results indicate that several negatively charged residues in the ligand-binding pocket of these receptors underpin the molecular basis for recognition of these small biogenic diamines in humans.
Scientists hope that the findings could also help us tackle major mood disorders. It is suspected that a few specific variations of TAAR6 are the cause of depression, bipolar and schizophrenic disorders in a sizeable population: evidence suggests one variant was found to affect how human subjects respond to antidepressants, while another variant of the receptor correlates with higher suicide risk.
The researchers suggested that patients with major mood disorders could be diagnosed using a new technique based on their findings. In the test, individuals are exposed to the “dead smell”, and then asked to rate their response to those scent stimuli. Any abnormal response could indicate that the patient may carry a mood disorder-linked variant of TAAR6 and therefore have an increased probability of certain mental conditions. Speculative as this may sound, the study might have provided researchers a new direction in tackling inheritable mental illness.
The Scent of Death (and Why It's Important) - Speaking of Chemistry. Credit: ACSReactions
Source: The Conversation