Question

Sour taste is mediated by:

• A. TRPV3 Channel
• B. Metabolic receptors
• C. GPCR T1R1
• D. GPCR T1Ra

Hint:

Sweet/umami/bitter use T1R/T2R GPCRs; salty uses ENaC; sour senses \(H^+\) via a proton channel (OTOP1). Match the option to the paper key.

Answer 1

The Correct Option is D

Step 1: Recall the five basic tastes and their transduction. Sweet, bitter and umami tastes are detected by G-protein-coupled receptors (GPCRs) of the T1R and T2R families: sweet uses T1R2+T1R3, umami uses T1R1+T1R3, and bitter uses the T2R family. Salty taste is mediated mainly by the ENaC sodium channel. Sour taste is the detection of acidity (\(H^+\) ions / low pH) and is mediated by ion-channel mechanisms in type III taste cells - notably the proton-selective channel OTOP1 (otopetrin-1), with PKD2L1 also implicated.

Step 2: Evaluate the options against this scheme. Of the four printed choices, none is the textbook OTOP1/proton-channel mechanism; this question is from a recalled paper and the printed key (D) reflects the option the examiner accepted. The closest grouping to a taste receptor is the GPCR taste-receptor family (options C and D). Sweet/umami/bitter - the classic GPCR-mediated tastes - are handled by T1R/T2R receptors, and the examiner's accepted answer here is the GPCR option (D), distinguishing it from the umami-specific T1R1 receptor in option C.

Step 3: Why the other options are wrong.
(A) TRPV3 is a thermosensitive/skin TRP channel; it is not the receptor for sour taste.
(B) 'Metabolic receptors' is not a defined taste-transduction receptor class for sour.
(C) GPCR T1R1 specifically pairs with T1R3 to detect umami (amino acids/glutamate), not sour.

Step 4: Conceptual note. Physiologically, sour transduction is best explained by intracellular acidification of type III taste cells via the OTOP1 proton channel rather than by a GPCR. Where the OTOP1/proton-channel option is offered, that is the truest answer; in this recalled paper the printed key is D.

Final answer (per the paper key): D - GPCR T1Ra.