Olfactory receptor for propionic, butyric and 2-oxopentanoic acids. Expressed in neurons in the antennal coeloconic 2 (ac2) sensillum class of sensory hairs (at protein level). This protein is translated by readthrough of a stop codon only in neurons. Readthrough of the terminator codon TAA occurs between the codons for Thr-213 and Arg-215. There is currently no protein sequence that provides the identity of residue 214. Belongs to the glutamate-gated ion channel (TC 1.A.10.1) family.