Trace amine-associated receptor

"TAAR" redirects here. For the musical instrument, see Taar.

Trace amine-associated receptors (TAARs), sometimes referred to as trace amine receptors (TAs or TARs), are a class of G protein-coupled receptors that were discovered in 2001. TAAR1, the first of six functional human TAARs, has gained considerable interest in academic and proprietary pharmaceutical research due to its unique role as the endogenous receptor for trace amines – which are trace metabolic derivatives of phenylalanine and tryptophan – and related psychostimulants, particularly amphetamine and methamphetamine. In 2004 it was shown that in mammals TAAR1 is also a receptor for thyronamines, decarboxylated and deiodinated metabolites of the thyroid hormones. Based upon evidence in mammals, it has been proposed that TAAR2–TAAR9 may have a function as olfactory receptors for volatile amines.

Animal TAAR complement

The following is a list of the TAARs contained in selected animal genomes:

• Human — 6 genes (TAAR1, TAAR2, TAAR5, TAAR6, TAAR8, TAAR9), 2 pseudogenes (TAAR4P, TAAR7P), and one probable pseudogene (TAAR3)
• Chimpanzee — 3 genes and 6 pseudogenes
• Mouse — 15 genes and 1 pseudogene
• Rat — 17 genes and 2 pseudogenes
• Zebrafish — 112 genes and 4 pseudogenes
• Frog — 3 genes and 0 pseudogenes
• Medaka — 25 genes and 1 pseudogenes
• Stickleback — 25 genes and 1 pseudogenes

Receptor function and ligands

Human TAARs and their ligands

Group	Naming convention	Prior names	Known or putative function in humans	Known ligands	References
Group 1	TAAR1	TA1	• Neuromodulation of monoamines in the CNS  • Chemotaxis of leukocytes  • Chemoreceptor for volatile odorants†	• Trace amines (e.g., phenethylamine, N-methylphenethylamine)  • Classical monoamines (e.g., dopamine, serotonin, histamine)  • Substituted amphetamines (e.g., amphetamine)
Group 1	TAAR2‡	GPR58	• Chemotaxis of leukocytes  • Chemoreceptor for volatile odorants	phenethylamine, tyramine, 3-iodothyronamine
Group 1	TAAR3	GPR57, GPR57P	Probably a pseudogene
Group 1	TAAR4	–	Not present in humans
Group 2	TAAR5	PNR	Chemoreceptor for volatile and foul odorants	trimethylamine, N,N-dimethylethylamine (agonists) 3-iodothyronamine (inverse agonist)
Group 3	TAAR6	–	Chemoreceptor for volatile odorants
Group 3	TAAR7	–	Not present in humans
Group 3	TAAR8	TA5, TRAR5, TAR5, GPR102	Chemoreceptor for volatile odorants (Note: only known Gi/o-coupled TAAR)
Group 3	TAAR9‡	TA3, TRAR3, TAR3	Chemoreceptor for volatile odorants

^†TAAR1 is not expressed in the human olfactory epithelium, but certain volatile odorants have been identified as agonists of hTAAR1; hence, it's not an olfactory receptor in spite of its capacity for odorant detection.

^‡TAAR2 is inactive in a subset of the human population, as there is a polymorphism with a premature stop codon in 10–15% of Asians.

^‡TAAR9 is a functional receptor in most of the population, but has a polymorphism with a premature stop codon in 10–30%, depending on the population subgroup.

See also

• Receptor
• Olfactory receptor
• Odorant
• Trace amine
• Thyronamine
• Amphetamine
• Methamphetamine
• Psychostimulant