An evolutionary conserved olfactory receptor for foodborne and semiochemical alkylpyrazines

Abstract

Molecular recognition is a fundamental principle in biological systems. The olfactory detection of both food and predators via ecological relevant odorant cues are abilities of eminent evolutionary significance for many species. Pyrazines are such volatile cues, some of which act as both human‐centered key food odorants (KFOs) and semiochemicals. A pyrazine‐selective odorant receptor has been elusive. Here we screened 2,3,5‐trimethylpyrazine, a KFO and semiochemical, and 2,5‐dihydro‐2,4,5‐trimethylthiazoline, an innate fear‐associated non‐KFO, against 616 human odorant receptor variants, in a cell‐based luminescence assay. OR5K1 emerged as sole responding receptor. Tested against a comprehensive collection of 178 KFOs, we newly identified 18 pyrazines and (2R/2S)‐4‐methoxy‐2,5‐dimethylfuran‐3(2H)‐one as agonists. Notably, OR5K1 orthologs in mouse and domesticated species displayed a human‐like, potency‐ranked activation pattern of pyrazines, suggesting a domestication‐led co‐evolution of OR5K1 and its orthologs. In summary, OR5K1 is a specialized olfactory receptor across mammals for the detection of pyrazine‐based key food odors and semiochemicals.

Modeling the Orthosteric Binding Site of the G Protein-Coupled Odorant Receptor OR5K1

“…Interestingly, in the screening of pyrazines, the mixture of isomers 2-ethyl-3,5(6)-dimethylpyrazine was found to activate OR5K1 with an EC50 of 21.18 μM. 50 In this work, we isolated the mixture and tested the individual isomers against OR5K1. We found that 2-ethyl-3,6-dimethylpyrazine (compound 2 ) has an EC 50 of 14.85 μM, while 2-ethyl-3,5-dimethylpyrazine (compound 13 ) could not be measured to saturation with the concentration range available.…”

“…Most ORs are still orphan and the receptive range of a few ORs has been characterized until now. In this paper, we used the recently published ligand information on OR5K1 50 to model and refine the OR5K1 orthosteric binding site. We used a multi-template homology modeling approach, as previously suggested to be a successful strategy for OR modeling.…”

“…OR5K1 has been recently characterized as the specialized OR for the detection of pyrazine-based key food odorants and semiochemicals. 50 We investigated the interaction of the set of identified agonists within the binding site of OR5K1 and used ligand information and mutagenesis data to guide the model refinement process.…”

“…Data for compounds 1, 3-12 are retrieved from literature,50 while data for compounds 2 and 13 were tested in this work.…”

“…SiteMap tool (Schrödinger Release 2021-3: SiteMap, Schrödinger, LLC, New York, NY, 2021) was used to characterize the binding cavities of both models. The compounds used in the screening byMarcinek et al were used for the model evaluation 50. However, we excluded from this set 54 molecules employed as a mixture of isomers.…”