Allosteric modulation of a human odorant receptor

Deciphering olfactory receptor binding mechanisms: a structural and dynamic perspective on olfactory receptors

Olfactory receptors, classified as G-protein coupled receptors (GPCRs), have been a subject of scientific inquiry since the early 1950s. Historically, investigations into the sensory mechanisms of olfactory receptors were often confined to behavioral characteristics in model organisms or the expression of related proteins and genes. However, with the development of cryo-electron microscopy techniques, it has gradually become possible to decipher the specific structures of olfactory receptors in insects and humans. This has provided new insights into the binding mechanisms between odor molecules and olfactory receptors. Furthermore, due to the rapid advancements in related fields such as computer simulations, the prediction and exploration of odor molecule binding to olfactory receptors have been progressively achieved through molecular dynamics simulations. Through this comprehensive review, we aim to provide a thorough analysis of research related to the binding mechanisms between odor molecules and olfactory receptors from the perspectives of structural biology and molecular dynamics simulations. Finally, we will provide an outlook on the future of research in the field of olfactory receptor sensory mechanisms.

Identification of Compounds That Contribute to Consumer Aroma Liking of Roasted American-European Hybrid Hazelnuts

New interspecific hybrid hazelnut crosses between American (Corylus americana) and European (Corylus avellana) hazelnuts are being developed to support a commercial industry in the Midwest region of the United States. In this study, volatile compounds that impact consumer aroma liking of roasted hybrid hazelnuts (C. americana × C. avellana) were investigated by targeted and nontargeted GC/MS flavoromics. Chemical profiles from 10 roasted hybrid hazelnut samples were modeled with consumer aroma liking scores by orthogonal partial least-squares with good fit and predictive performance (R2 ≥ 0.92, Q2 ≥ 0.82, RMSECV = 0.2). Top ranked predictors positively correlated with liking included 12 aroma compounds and 4 profiled volatiles for the targeted and nontargeted methods, respectively. Sensory recombination testing of hazelnut samples with addition of the 12 predictive odorants was preferred by consumers (p < 0.001, Δ aroma liking = 2.2 on 9-point scale) and perceived as more roasty, nutty, and sweet compared to the control (p < 0.05). Addition of the 4 predictive volatiles at subthreshold levels also was preferred (p = 0.02) and perceived as less earthy and mushroom like than the control (p < 0.05).

Intracellular Allosteric Antagonist of the Olfactory Receptor OR51E2

Olfactory receptors are members of class A (rhodopsin-like) family of G protein-coupled receptors (GPCRs). Their expression and function have been increasingly studied in nonolfactory tissues, and many have been identified as potential therapeutic targets. In this manuscript, we focus on the discovery of novel ligands for the olfactory receptor family 51 subfamily E2 (OR51E2). We performed an artificial intelligence-based virtual drug screen of a ∼2.2 million small molecule library. Cell-based functional assay identified compound 80 (C80) as an antagonist and inverse agonist, and detailed pharmacological analysis revealed C80 acts as a negative allosteric modulator by significantly decreasing the agonist efficacy, while having a minimal effect on receptor affinity for agonist. C80 binds to an allosteric binding site formed by a network of nine residues localized in the intracellular parts of transmembrane domains 3, 5, 6, 7, and H8, which also partially overlaps with a G protein binding site. Mutational experiments of residues involved in C80 binding uncovered the significance of the C2406.37 position in blocking the activation-related conformational change and keeping the receptor in the inactive form. Our study provides a mechanistic understanding of the negative allosteric action of C80 on agonist-ctivated OR51E2. We believe the identification of the antagonist of OR51E2 will enable a multitude of studies aiming to determine the functional role of this receptor in specific biologic processes. SIGNIFICANCE STATEMENT: OR51E2 has been implicated in various biological processes, and its antagonists that can effectively modulate its activity have therapeutic potential. Here we report the discovery of a negative allosteric modulator of OR51E2 and provide a mechanistic understanding of its action. We demonstrate that this modulator has an inhibitory effect on the efficacy of the agonist for the receptor and reveal a network of nine residues that constitute its binding pocket, which also partially overlaps with the G protein binding site.

The trilogy of human musk receptors: linking receptor activation, genotype, and sensory perception

The scent of musk plays a unique role in the history of perfumery. Musk odorants comprise 6 diverse chemical classes and perception differences in strength and quality among human panelists have long puzzled the field of olfaction research. Three odorant receptors (OR) had recently been described for musk odorants: OR5AN1, OR1N2, and OR5A2. High functional expression of the difficult-to-express human OR5A2 was achieved by a modification of the C-terminal domain and the link between sensory perception and receptor activation for the trilogy of these receptors and their key genetic variants was investigated: All 3 receptors detect only musky smelling compounds among 440 commercial fragrance compounds. OR5A2 is the key receptor for the classes of polycyclic and linear musks and for most macrocylic lactones. A single P172L substitution reduces the sensitivity of OR5A2 by around 50-fold. In parallel, human panelists homozygous for this mutation have around 40-60-fold higher sensory detection threshold for selective OR5A2 ligands. For macrocyclic lactones, OR5A2 could further be proven as the key OR by a strong correlation between in vitro activation and the sensory detection threshold in vivo. OR5AN1 is the dominant receptor for the perception of macrocyclic ketones such as muscone and some nitromusks, as panelists with a mutant OR5A2 are still equally sensitive to these ligands. Finally, OR1N2 appears to be an additional receptor involved in the perception of the natural (E)-ambrettolide. This study for the first time links OR activation to sensory perception and genetic polymorphisms for this unique class of odorants.

Metabolomic analysis for disclosing nutritional and therapeutic prospective of traditional rice cultivars of Cauvery deltaic region, India

Traditional rice is gaining popularity worldwide due to its high nutritional and pharmaceutical value, as well as its high resistance to abiotic and biotic stresses. This has attracted significant attention from breeders, nutritionists, and plant protection scientists in recent years. Hence, it is critical to investigate the grain metabolome to reveal germination and nutritional importance. This research aimed to explore non-targeted metabolites of five traditional rice varieties, viz., Chinnar, Chithiraikar, Karunguruvai, Kichili samba, and Thooyamalli, for their nutritional and therapeutic properties. Approximately 149 metabolites were identified using the National Institute of Standards and Technology (NIST) library and Human Metabolome Database (HMDB) and were grouped into 34 chemical classes. Major classes include fatty acids (31.1-56.3%), steroids and their derivatives (1.80-22.4%), dihydrofurans (8.98-11.6%), prenol lipids (0.66-4.44%), organooxygen compounds (0.12-6.45%), benzene and substituted derivatives (0.53-3.73%), glycerolipids (0.36-2.28%), and hydroxy acids and derivatives (0.03-2.70%). Significant variations in metabolite composition among the rice varieties were also observed through the combination of univariate and multivariate statistical analyses. Principal component analysis (PCA) reduced the dimensionality of 149 metabolites into five principle components (PCs), which explained 96% of the total variance. Two clusters were revealed by hierarchical cluster analysis, indicating the distinctiveness of the traditional varieties. Additionally, a partial least squares-discriminant analysis (PLS-DA) found 17 variables important in the projection (VIP) scores of metabolites. The findings of this study reveal the biochemical intricate and distinctive metabolomes of the traditional therapeutic rice varieties. This will serve as the foundation for future research on developing new rice varieties with traditional rice grain metabolisms to increase grain quality and production with various nutritional and therapeutic benefits.

An angiotensin converting enzyme homolog is required for volatile pheromone detection, odorant binding protein secretion and normal courtship behavior in Drosophila melanogaster

In many arthropods, including insects responsible for transmission of human diseases, behaviors that include mating, aggregation, and aggression are triggered by detection of pheromones. Extracellular odorant binding proteins are critical for pheromone detection in many insects and are secreted into the fluid bathing the olfactory neuron dendrites. In Drosophila melanogaster, the odorant binding protein LUSH is essential for normal sensitivity to the volatile sex pheromone, 11-cis vaccenyl acetate (cVA). Using a genetic screen for cVA pheromone insensitivity, we identified ANCE-3, a homolog of human angiotensin converting enzyme that is required for detection of cVA pheromone. The mutants have normal dose-response curves for food odors, although olfactory neuron amplitudes are reduced in all olfactory neurons examined. ance-3 mutants have profound delays in mating, and the courtship defects are primarily but not exclusively due to loss of ance-3 function in males. We demonstrate that ANCE-3 is required in the sensillae support cells for normal reproductive behavior, and that localization of odorant binding proteins to the sensillum lymph is blocked in the mutants. Expression of an ance-3 cDNA in sensillae support cells completely rescues the cVA responses, LUSH localization, and courtship defects. We show the courtship latency defects are not due to effects on olfactory neurons in the antenna nor mediated through ORCO receptors, but instead stem from ANCE-3-dependent effects on chemosensory sensillae in other body parts. These findings reveal an unexpected factor critical for pheromone detection with profound influence on reproductive behaviors.

Olfaction: Allosteric modulation

New research indicates that the odor-evoked responses of human olfactory receptors can be enhanced via the non-competitive binding of an allosteric modulator. This modulatory mechanism adds an additional layer of complexity to the peripheral encoding of odors.