TRPA is a family of

transient receptor potential Transient receptor potential channels (TRP channels) are a group of ion channels located mostly on the plasma membrane of numerous animal cell types. Most of these are grouped into two broad groups: Group 1 includes TRPC ( "C" for canonical), TR ...

ion channels. The TRPA family is made up of 7 subfamilies: TRPA1, TRPA- or TRPA1-like, TRPA5, painless, pyrexia, waterwitch, and HsTRPA. TRPA1 is the only subfamily widely expressed across animals, while the other subfamilies (collectively referred to as the basal clade) are largely absent in

deuterostomes Deuterostomia (; in Greek) are animals typically characterized by their anus forming before their mouth during embryonic development. The group's sister clade is Protostomia, animals whose digestive tract development is more varied. Some exampl ...

(and in the case of HsTRPA, only expressed in

hymenopteran Hymenoptera is a large order of insects, comprising the sawflies, wasps, bees, and ants. Over 150,000 living species of Hymenoptera have been described, in addition to over 2,000 extinct ones. Many of the species are parasitic. Females typica ...

insects). TRPA1s have been the most extensively studied subfamily; they typically contain 14 N-terminal

ankyrin Ankyrins are a family of proteins that mediate the attachment of integral membrane proteins to the spectrin-actin based membrane cytoskeleton. Ankyrins have binding sites for the beta subunit of spectrin and at least 12 families of integral mem ...

repeats and are believed to function as mechanical stress, temperature, and chemical sensors. TRPA1 is known to be activated by compounds such as

isothiocyanate In organic chemistry, isothiocyanate is the functional group , formed by substituting the oxygen in the isocyanate group with a sulfur. Many natural isothiocyanates from plants are produced by enzymatic conversion of metabolites called glucosi ...

(which are the pungent chemicals in substances such as

mustard oil Mustard oil can mean either the pressed oil used for cooking, or a pungent essential oil also known as volatile oil of mustard. The essential oil results from grinding mustard seed, mixing the grounds with water, and extracting the resulting vola ...

and

wasabi Wasabi ( Japanese: , , or , ; ''Eutrema japonicum'' or ''Wasabia japonica'') or Japanese horseradish is a plant of the family Brassicaceae, which also includes horseradish and mustard in other genera. The plant is native to Japan and the Russi ...

) and

Michael acceptor In organic chemistry, the Michael reaction or Michael addition is a reaction between a Michael donor (an enolate or other nucleophile) and a Michael acceptor (usually an α,β-unsaturated carbonyl) to produce a Michael adduct by creating a carbo ...

s (e.g.

cinnamaldehyde Cinnamaldehyde is an organic compound with the formula(C9H8O) C6H5CH=CHCHO. Occurring naturally as predominantly the ''trans'' (''E'') isomer, it gives cinnamon its flavor and odor. It is a phenylpropanoid that is naturally synthesized by the sh ...

). These compounds are capable of forming covalent chemical bonds with the protein's

cystein Cysteine (symbol Cys or C; ) is a semiessential proteinogenic amino acid with the formula . The thiol side chain in cysteine often participates in enzymatic reactions as a nucleophile. When present as a deprotonated catalytic residue, someti ...

s. Non-covalent activators of TRPA1 also exists, such as

methyl salicylate Methyl salicylate (oil of wintergreen or wintergreen oil) is an organic compound with the formula C8H8O3. It is the methyl ester of salicylic acid. It is a colorless, viscous liquid with a sweet, fruity odor reminiscent of root beer, but often a ...

, menthol, and the synthetic compound

PF-4840154 PF-4840154 is a pyrimidine derivative discovered by Pfizer at its Sandwich, Kent research center. The compound is a potent, selective activator of both the human (EC50 = 23 nM) and rat (EC50 = 97 nM) TRPA1 channels. This compound elicits nocicept ...

. The thermal sensitivity of TRPAs varies by species. For example, TRPA1 functions as a high-temperature sensor in insects and snakes, but as a cold sensor in mammals. The basal TRPAs have evolved some degree of thermal sensitivity as well: painless and pyrexia function in high-temperature sensing in

Drosophila melanogaster ''Drosophila melanogaster'' is a species of fly (the taxonomic order Diptera) in the family Drosophilidae. The species is often referred to as the fruit fly or lesser fruit fly, or less commonly the " vinegar fly" or "pomace fly". Starting with ...

, and the honey bee HsTRPA underwent

neofunctionalization Neofunctionalization, one of the possible outcomes of functional divergence, occurs when one gene copy, or paralog, takes on a totally new function after a gene duplication event. Neofunctionalization is an adaptive mutation process; meaning one ...

following its divergence from waterwitch, gaining function as a high-temperature sensor. TRPA1s promiscuity with respect to sensory modality has been the source of controversy, particularly when considering its ability to detect cold. More recent work has alternatively (or additionally) proposed that

reactive oxygen species In chemistry, reactive oxygen species (ROS) are highly reactive chemicals formed from diatomic oxygen (). Examples of ROS include peroxides, superoxide, hydroxyl radical, singlet oxygen, and alpha-oxygen. The reduction of molecular oxygen () p ...

activate TRPA1, across species.

References

External links

* * {{Transient receptor potential channel modulators Membrane proteins Ion channels