The Mouse Eugenol Odorant Receptor: Structural and Functional Plasticity of a Broadly Tuned Odorant Binding Pocket

Abstract

Molecular interactions of odorants with their olfactory receptors (ORs) are of central importance for the ability of the mammalian olfactory system to detect and discriminate a vast variety of odors with a limited set of receptors. How a particular OR binds and distinguishes different odorant molecules remains largely unknown on a structural basis. Here we investigated this question for the mouse eugenol receptor (mOR-EG). By screening a large odorant library, we discovered a wide range of chemical structures activating the receptor in heterologous mammalian cells. Potent agonists comprise (i) benzene, (ii) cyclohexane, or (iii) polycyclic structures substituted with alcohol, aldehyde, keto, ether, or esterified carboxylic groups. To detect those amino acids within the receptor that are in contact with a particular bound odorant molecule, we investigated how distinct mOR-EG point mutants were activated by the different odorant agonists found for the wild-type receptor. We identified 11 amino acids as a part of the receptor's ligand binding pocket. Molecular modeling predicted 10 of these residues in transmembrane helices TM3-TM6 and one in the extracellular loop between TM2 and TM3. These amino acids participate in odorant binding with variable importance depending on the type of odorant, revealing functional "fingerprints" of ligand-receptor interactions.

Responsiveness of G protein-coupled odorant receptors is partially attributed to the activation mechanism

“…Unlike most nonolfactory GPCRs, which use ionic or hydrogen bond interactions to ensure selectivity and sensitivity in binding their agonists or antagonists (22), ORs bind to their ligands via much weaker van der Waals interactions (14,16,23). It is conceivable that at least some ORs have a permissive binding The total response is the sum of the responses to all five odorants at 300 μM, normalized to that of WT MOR256-3 tested on the same plate and corrected for surface expression.…”

Modeling of mammalian olfactory receptors and docking of odorants

“…After the elucidation of a second GPCR structure in 2007, that of the human β2 adrenergic receptor, questions related to the applicability of rhodopsin as a model for other GPCR structures were eventually settled, and most models were then based on the homology modeling approach using the available high-resolution GPCR structures as templates. After 2005, the results of the OR modeling and ligand docking in silico simulations were systematically validated by site-directed mutagenesis experiments and functional assays in an effort to better understand the characteristics of ligand recognition by ORs [screening of large odorant libraries and determination of functional fingerprints (Baud et al 2010), characterization of 'odotypes' (Schmiedeberg et al 2007;Stary et al 2007), correlation between the ligand concentration required for 50 % activation of the receptor (EC50), and the computed binding energy (Kurland et al 2010), among others]. Due to the difficulty of aligning some of the OR TMHs, most proposed models 2.8 Å bovine rhodopsin 3D structure Schmiedeberg et al 2007 This work is related to that in (Stary et al 2007).…”

“…Use of site-directed mutagenesis to locate functionally important residues. Mapping of relevant residues in TMH3, 5, and 6. mOR-EG 2.4 Å β2-adrenergic receptor 3D structure 2010 Baud et al 2010 Screening of a large odorant library allowed the authors to discover a wide range of chemical compounds activating mOR-EG. Residues responsible for the ligand recognition were probed by mutagenesis experiments.…”

Prediction of a Ligand‐Binding Niche within a Human Olfactory Receptor by Combining Site‐Directed Mutagenesis with Dynamic Homology Modeling

“…[19][20][21][22] For such receptor-based and mixed approaches, the X-ray structures of seven GPCRs have been solved to date, [23][24][25][26][27][28][29][30][31][32] but none for ORs. Previous studies have used static structural models of different ORs based on a rhodopsin [12][13][14][15][16][17][18][19][20][21] and a b 2 -adrenergic receptor (B2AR) [33] template. However, most odorants are highly flexible, so assessment of the ligand/protein dynamics might be of crucial importance in understanding ligand recognition by ORs.…”