TRPA1 and Sharp Pungency
TRPA1 (Transient Receptor Potential Ankyrin 1) is a cation channel on sensory neurons that responds to electrophilic compounds — those that covalently modify cysteine and lysine residues in the channel's N-terminal ankyrin repeat domain. It is distinct from TRPV1 and produces a sharper, more acrid pungency than capsaicin.
TRPA1 Ligands
The most potent natural TRPA1 agonists are allicin (garlic, ~1 µM EC₅₀), sinigrin hydrolysis products (mustard, wasabi), cinnamaldehyde (cinnamon), acrolein, and 4-hydroxynonenal. Unlike capsaicin's reversible TRPV1 binding, allicin and other electrophilic ligands activate TRPA1 by covalently modifying Cys621, Cys641, and Cys665 — a modification that is slowly reversed.
IFI-P Axis
The IFI-P (Sharp) axis quantifies TRPA1 activation relative to allicin at saturation. It is relevant for constructs engineering the alliinase pathway in alliums (garlic pungency engineering), sinigrin content in brassicas, or cinnamaldehyde in cinnamon-flavor applications. High IFI-P with low IFI-H gives a 'hot mustard' heat profile; combined high IFI-P and IFI-H produces the complex layered pungency of some Southeast Asian cuisines.