ABSTRACT
This study presents a comprehensive analysis of the dimerization interfaces of fly GSTs through sequence alignment. Our investigation revealed GSTE1 as a particularly intriguing target, providing valuable insights into the variations within Delta and Epsilon GST interfaces. The X-ray structure of GSTE1 was determined, unveiling remarkable thermal stability and a distinctive dimerization interface. Utilizing circular dichroism, we assessed the thermal stability of GSTE1 and other Drosophila GSTs with resolved X-ray structures. The subsequent examination of GST dimer stability correlated with the dimerization interface supported by findings from X-ray structural analysis and thermal stability measurements. Our discussion extends to the broader context of GST dimer interfaces, offering a generalized perspective on their stability. This research enhances our understanding of the structural and thermodynamic aspects of GST dimerization, contributing valuable insights to the field.
Subject(s)
Glutathione Transferase , Protein Multimerization , Thermodynamics , Animals , Glutathione Transferase/chemistry , Glutathione Transferase/metabolism , Glutathione Transferase/genetics , Drosophila Proteins/chemistry , Drosophila Proteins/metabolism , Crystallography, X-Ray , Drosophila melanogaster/enzymology , Models, Molecular , Amino Acid Sequence , Drosophila/enzymologyABSTRACT
ß C-S lyases (ß-CSLs; EC 4.4.1.8) are enzymes catalyzing the dissociation of ß carbon-sulfur bonds of cysteine S-conjugates to produce odorant metabolites with a free thiol group. These enzymes are increasingly studied for their role in flavor generation in a variety of food products, whether these processes occur directly in plants, by microbial ß-CSLs during fermentation, or in the mouth under the action of the oral microbiota. Microbial ß-CSLs react with sulfur aroma precursors present in beverages, vegetables, fruits, or aromatic herbs like hop but also potentially with some precursors formed through Maillard reactions in cooked foods such as meat or coffee. ß-CSLs from microorganisms like yeasts and lactic acid bacteria have been studied for their role in the release of polyfunctional thiols in wine and beer during fermentation. In addition, ß-CSLs from microorganisms of the human oral cavity were shown to metabolize similar precursors and to produce aroma in the mouth with an impact on retro-olfaction. This review summarizes the current knowledge on ß-CSLs involved in flavor generation with a focus on enzymes from microbial species present either in the fermentative processes or in the oral cavity. This paper highlights the importance of this enzyme family in the food continuum, from production to consumption, and offers new perspectives concerning the utilization of ß-CSLs as a flavor enhancer.
Subject(s)
Fermentation , Flavoring Agents , Humans , Flavoring Agents/metabolism , Carbon-Sulfur Lyases/metabolism , Bacteria/enzymology , Bacteria/metabolism , TasteABSTRACT
Nasal xenobiotic metabolizing enzymes (XMEs) are important for the sense of smell because they influence odorant availability and quality. Since the major part of the human nasal cavity is lined by a respiratory mucosa, we hypothesized that this tissue contributed to nasal odorant metabolism through XME activity. Thus, we built human respiratory tissue models and characterized the XME profiles using single-cell RNA sequencing. We focused on the XMEs dicarbonyl and l-xylulose reductase, aldehyde dehydrogenase (ALDH) 1A1, and ALDH3A1, which play a role in food odorant metabolism. We demonstrated protein abundance and localization in the tissue models and showed the metabolic activity of the corresponding enzyme families by exposing the models to the odorants 3,4-hexandione and benzaldehyde. Using gas chromatography coupled with mass spectrometry, we observed, for example, a significantly higher formation of the corresponding metabolites 4-hydroxy-3-hexanone (39.03 ± 1.5%, p = 0.0022), benzyl alcohol (10.05 ± 0.88%, p = 0.0008), and benzoic acid (8.49 ± 0.57%, p = 0.0004) in odorant-treated tissue models compared to untreated controls (0 ± 0, 0.12 ± 0.12, and 0.18 ± 0.18%, respectively). This is the first study that reveals the XME profile of tissue-engineered human respiratory mucosa models and demonstrates their suitability to study nasal odorant metabolism.
Subject(s)
Odorants , Respiratory Mucosa , Humans , Odorants/analysis , Respiratory Mucosa/metabolism , Models, Biological , Gas Chromatography-Mass Spectrometry , Aldehyde Dehydrogenase 1 Family/metabolism , Aldehyde Dehydrogenase 1 Family/genetics , Xenobiotics/metabolismABSTRACT
Glutathione transferases are xenobiotic-metabolizing enzymes with both glutathione-conjugation and ligandin roles. GSTs are present in chemosensory tissues and fluids of the nasal/oral cavities where they protect tissues from exogenous compounds, including food molecules. In the present study, we explored the presence of the omega-class glutathione transferase (GSTO1) in the rat oral cavity. Using immunohistochemistry, GSTO1 expression was found in taste bud cells of the tongue epithelium and buccal cells of the oral epithelium. Buccal and lingual extracts exhibited thiol-transferase activity (4.9 ± 0.1 and 1.8 ± 0.1 µM/s/mg, respectively). A slight reduction from 4.9 ± 0.1 to 4.2 ± 0.1 µM/s/mg (p < 0.05; Student's t test) was observed in the buccal extract with 100 µM GSTO1-IN-1, a specific inhibitor of GSTO1. RnGSTO1 exhibited the usual activities of omega GSTs, i.e., thiol-transferase (catalytic efficiency of 8.9 × 104 M-1·s-1), and phenacyl-glutathione reductase (catalytic efficiency of 8.9 × 105 M-1·s-1) activities, similar to human GSTO1. RnGSTO1 interacts with food phytochemicals, including bitter compounds such as luteolin (Ki = 3.3 ± 1.9 µM). Crystal structure analysis suggests that luteolin most probably binds to RnGSTO1 ligandin site. Our results suggest that GSTO1 could interact with food phytochemicals in the oral cavity.
Subject(s)
Glutathione Transferase , Luteolin , Rats , Animals , Humans , Glutathione Transferase/metabolism , Mouth Mucosa/metabolism , Sulfhydryl Compounds , Glutathione/metabolismABSTRACT
[This corrects the article DOI: 10.1371/journal.pone.0249029.].
ABSTRACT
The mucosal pellicle (MP) is a biological film protecting the oral mucosa. It is composed of bounded salivary proteins and transmembrane mucin MUC1 expressed by oral epithelial cells. Previous research indicates that MUC1 expression enhances the binding of the main salivary protein forming the MP, MUC5B. This study investigated the influence of MUC1 structure on MP formation. A TR146 cell line, which does not express MUC1 natively, was stably transfected with genes coding for three MUC1 isoforms differing in the structure of the two main extracellular domains: the VNTR domain, exhibiting a variable number of tandem repeats, and the SEA domain, maintaining the two bound subunits of MUC1. Semi-quantification of MUC1 using dot blot chemiluminescence showed comparable expression levels in all transfected cell lines. Semi-quantification of MUC5B by immunostaining after incubation with saliva revealed that MUC1 expression significantly increased MUC5B adsorption. Neither the VNTR domain nor the SEA domain was influenced MUC5B anchoring, suggesting the key role of the MUC1 N-terminal domain. AFM-IR nanospectroscopy revealed discernible shifts indicative of changes in the chemical properties at the cell surface due to the expression of the MUC1 isoform. Furthermore, the observed chemical shifts suggest the involvement of hydrophobic effects in the interaction between MUC1 and salivary proteins.
ABSTRACT
Aroma is among of the most important criteria that indicate the quality of food and beverage products. Aroma compounds can be found as free molecules or glycosides. Notably, a significant portion of aroma precursors accumulates in numerous food products as nonvolatile and flavorless glycoconjugates, termed glycosidic aroma precursors. When subjected to enzymatic hydrolysis, these seemingly inert, nonvolatile glycosides undergo transformation into fragrant volatiles or volatiles that can generate odor-active compounds during food processing. In this context, microbial ß-glucosidases play a pivotal role in enhancing or compromising the development of flavors during food and beverage processing. ß-glucosidases derived from bacteria and yeast can be utilized to modulate the concentration of particular aroma and taste compounds, such as bitterness, which can be decreased through hydrolysis by glycosidases. Furthermore, oral microbiota can influence flavor perception by releasing volatile compounds that can enhance or alter the perception of food products. In this review, considering the glycosidic flavor precursors present in diverse food and beverage products, we underscore the significance of glycosidases with various origins. Subsequently, we delve into emerging insights regarding the release of aroma within the human oral cavity due to the activity of oral microbial glycosidases.
ABSTRACT
Olfaction is a multi-step process. At a peripheral level, nasal odorant metabolism contributes to olfaction via signal termination, variation, and regulation. We summarize current techniques used to investigate nasal odorant metabolism and give an outlook on future approaches, such as nasal tissue models and their potential contributions in future research directions.
Subject(s)
Odorants , SmellABSTRACT
In insects such as Drosophila melanogaster, flight guidance is based on converging sensory information provided by several modalities, including chemoperception. Drosophila flies are particularly attracted by complex odors constituting volatile molecules from yeast, pheromones and microbe-metabolized food. Based on a recent study revealing that adult male courtship behavior can be affected by early preimaginal exposure to maternally transmitted egg factors, we wondered whether a similar exposure could affect free-flight odor tracking in flies of both sexes. Our main experiment consisted of testing flies differently conditioned during preimaginal development in a wind tunnel. Each fly was presented with a dual choice of food labeled by groups of each sex of D. melanogaster or D. simulans flies. The combined effect of food with the cis-vaccenyl acetate pheromone (cVA), which is involved in aggregation behavior, was also measured. Moreover, we used the headspace method to determine the "odorant" identity of the different labeled foods tested. We also measured the antennal electrophysiological response to cVA in females and males resulting from the different preimaginal conditioning procedures. Our data indicate that flies differentially modulated their flight response (take off, flight duration, food landing and preference) according to sex, conditioning and food choice. Our headspace analysis revealed that many food-derived volatile molecules diverged between sexes and species. Antennal responses to cVA showed clear sex-specific variation for conditioned flies but not for control flies. In summary, our study indicates that preimaginal conditioning can affect Drosophila free flight behavior in a sex-specific manner.
Subject(s)
Drosophila Proteins , Drosophila melanogaster , Male , Animals , Female , Drosophila melanogaster/physiology , Odorants , Drosophila , Smell/physiology , Drosophila Proteins/pharmacology , Pheromones/pharmacologyABSTRACT
Oxidoreductases are major enzymes of xenobiotic metabolism. Consequently, they are essential in the chemoprotection of the human body. Many xenobiotic metabolism enzymes have been shown to be involved in chemosensory tissue protection. Among them, some were additionally shown to be involved in chemosensory perception, acting in signal termination as well as in the generation of metabolites that change the activation pattern of chemosensory receptors. Oxidoreductases, especially aldehyde dehydrogenases and aldo-keto reductases, are the first barrier against aldehyde compounds, which include numerous odorants. Using a mass spectrometry approach, we characterized the most highly expressed members of these families in the human nasal mucus sampled in the olfactory vicinity. Their expression was also demonstrated using immunohistochemistry in human epitheliums sampled in the olfactory vicinity. Recombinant enzymes corresponding to three highly expressed human oxidoreductases (ALDH1A1, ALDH3A1, AKR1B10) were used to demonstrate the high enzymatic activity of these enzymes toward aldehyde odorants. The structureâfunction relationship set based on the enzymatic parameters characterization of a series of aldehyde odorant compounds was supported by the X-ray structure resolution of human ALDH3A1 in complex with octanal.
Subject(s)
Oxidoreductases , Receptors, Odorant , Humans , Oxidoreductases/metabolism , Odorants/analysis , Xenobiotics/metabolism , Smell/physiology , Respiratory System/metabolism , Alcohol Oxidoreductases/metabolism , Receptors, Odorant/genetics , Receptors, Odorant/metabolismABSTRACT
Glutathione transferases (GSTs) are ubiquitous key enzymes with different activities as transferases or isomerases. As key detoxifying enzymes, GSTs are expressed in the chemosensory organs. They fulfill an essential protective role because the chemosensory organs are located in the main entry paths of exogenous compounds within the body. In addition to this protective function, they modulate the perception process by metabolizing exogenous molecules, including tastants and odorants. Chemosensory detection involves the interaction of chemosensory molecules with receptors. GST contributes to signal termination by metabolizing these molecules. By reducing the concentration of chemosensory molecules before receptor binding, GST modulates receptor activation and, therefore, the perception of these molecules. The balance of chemoperception by GSTs has been shown in insects as well as in mammals, although their chemosensory systems are not evolutionarily connected. This review will provide knowledge supporting the involvement of GSTs in chemoperception, describing their localization in these systems as well as their enzymatic capacity toward odorants, sapid molecules, and pheromones in insects and mammals. Their different roles in chemosensory organs will be discussed in light of the evolutionary advantage of the coupling of the detoxification system and chemosensory system through GSTs.
Subject(s)
Glutathione Transferase , Mammals , Animals , Glutathione Transferase/metabolism , Mammals/metabolism , Protein Binding , Insecta/metabolism , Glutathione/metabolismABSTRACT
Within the peripheral olfactory process, odorant metabolizing enzymes are involved in the active biotransformation of odorants, thus influencing the intensity and quality of the signal, but little evidence exists in humans. Here, we characterized the fast nasal metabolism of the food aroma pentane-2,3-dione in vivo and identified two resulting metabolites in the nasal-exhaled air, supporting the metabolizing role of the dicarbonyl/l-xylulose reductase. We showed in vitro, using the recombinant enzyme, that pentane-2,3-dione metabolism was inhibited by a second odorant (e.g., butanoic acid) according to an odorant-odorant competitive metabolic mechanism. Hypothesizing that such mechanism exists in vivo, pentane-2,3-dione, presented with a competitive odorant, both at subthreshold concentrations, was actually significantly perceived, suggesting an increase in its nasal availability. Our results, suggesting that odorant metabolizing enzymes can balance the relative detection of odorants in a mixture, in turn influencing the intensity of the signal, should be considered to better manage flavor perception in food.
Subject(s)
Odorants , Receptors, Odorant , Humans , Pentanes , Receptors, Odorant/metabolism , SmellABSTRACT
Odorants are relatively small molecules which are easily taken up and distributed in the human body. Despite their relevance in everyday life, however, only a limited amount of evidence about their metabolism, pathways, and bioactivities in the human body exists. With this Review, we aim to encourage future interdisciplinary research on the function and mechanisms of the biotransformation of odorants, involving different disciplines such as nutrition, medicine, biochemistry, chemistry, and sensory sciences. Starting with a general overview of the different ways of odorant uptake and enzymes involved in the metabolism of odorants, a more precise description of biotransformation processes and their function in the oral cavity, the nose, the lower respiratory tract (LRT), and the gastrointestinal tract (GIT) is given together with an overview of the different routes of odorant excretion. Finally, perspectives for future research are discussed.
Subject(s)
Odorants , Receptors, Odorant , Biological Transport , Humans , Mouth , Receptors, Odorant/metabolism , SmellABSTRACT
The molecules that elicit taste sensation are perceived by interacting with the taste receptors located in the taste buds. Enzymes involved in the detoxification processes are found in saliva as well as in type II cells, where taste receptors, including bitter taste receptors, are located. These enzymes are known to interact with a large panel of molecules. To explore a possible link between these enzymes and bitter taste perception, we demonstrate that salivary glutathione transferases (GSTA1 and GSTP1) can metabolize bitter molecules. To support these abilities, we solve three X-ray structures of these enzymes in complexes with isothiocyanates. Salivary GSTA1 and GSTP1 are expressed in a large panel of subjects. Additionally, GSTA1 levels in the saliva of people suffering from taste disorders are significantly lower than those in the saliva of the control group.
Subject(s)
Taste Buds , Taste , Humans , Saliva/chemistry , Taste PerceptionABSTRACT
The oral cavity is an entry path into the body, enabling the intake of nutrients but also leading to the ingestion of harmful substances. Thus, saliva and oral tissues contain enzyme systems that enable the early neutralization of xenobiotics as soon as they enter the body. Based on recently published oral proteomic data from several research groups, this review identifies and compiles the primary detoxification enzymes (also known as xenobiotic-metabolizing enzymes) present in saliva and the oral epithelium. The functions and the metabolic activity of these enzymes are presented. Then, the activity of these enzymes in saliva, which is an extracellular fluid, is discussed with regard to the salivary parameters. The next part of the review presents research evidencing oral metabolization of aroma compounds and the putative involved enzymes. The last part discusses the potential role of these enzymatic reactions on the perception of aroma compounds in light of recent pieces of evidence of in vivo oral metabolization of aroma compounds affecting their release in mouth and their perception. Thus, this review highlights different enzymes appearing as relevant to explain aroma metabolism in the oral cavity. It also points out that further works are needed to unravel the effect of the oral enzymatic detoxification system on the perception of food flavor in the context of the consumption of complex food matrices, while considering the impact of food oral processing. Thus, it constitutes a basis to explore these biochemical mechanisms and their impact on flavor perception.
Subject(s)
Odorants , Proteome , Mouth , Proteomics , SalivaABSTRACT
Odorant metabolizing enzymes (OMEs) are expressed in the olfactory epithelium (OE) where they play a significant role in the peripheral olfactory process by catalyzing the fast biotransformation of odorants leading either to their elimination or to the synthesis of new odorant stimuli. The large family of OMEs gathers different classes which interact with a myriad of odorants alike and complementary to olfactory receptors. Thus, it is necessary to increase our knowledge on OMEs to better understand their function in the physiological process of olfaction. This study focused on a major olfactory UDP-glucuronosyltransferase (UGT): UGT2A1. Immunohistochemistry and immunogold electronic microscopy allowed to localize its expression in the apical part of the sustentacular cells and originally at the plasma membrane of the olfactory cilia of the olfactory sensory neurons, both locations in close vicinity with olfactory receptors. Moreover, using electroolfactogram, we showed that a treatment of the OE with beta-glucuronidase, an enzyme which counterbalance the UGTs activity, increased the response to eugenol which is a strong odorant UGT substrate. Altogether, the results supported the function of the olfactory UGTs in the vertebrate olfactory perireceptor process.
Subject(s)
Glucuronosyltransferase/metabolism , Odorants , Smell/physiology , Animals , Eugenol/pharmacology , Glucuronidase/metabolism , Glucuronides/metabolism , Male , Olfactory Mucosa/drug effects , Olfactory Mucosa/metabolism , Olfactory Mucosa/ultrastructure , Pentanols/pharmacology , Rats, Wistar , Receptors, Odorant/metabolism , Smell/drug effectsABSTRACT
Xenobiotic metabolizing enzymes and other proteins, including odorant-binding proteins located in the nasal epithelium and mucus, participate in a series of processes modulating the concentration of odorants in the environment of olfactory receptors (ORs) and finely impact odor perception. These enzymes and transporters are thought to participate in odorant degradation or transport. Odorant biotransformation results in 1) changes in the odorant quantity up to their clearance and the termination of signaling and 2) the formation of new odorant stimuli (metabolites). Enzymes, such as cytochrome P450 and glutathione transferases (GSTs), have been proposed to participate in odorant clearance in insects and mammals as odorant metabolizing enzymes. This study aims to explore the function of GSTs in human olfaction. Using immunohistochemical methods, GSTs were found to be localized in human tissues surrounding the olfactory epithelium. Then, the activity of 2 members of the GST family toward odorants was measured using heterologously expressed enzymes. The interactions/reactions with odorants were further characterized using a combination of enzymatic techniques. Furthermore, the structure of the complex between human GSTA1 and the glutathione conjugate of an odorant was determined by X-ray crystallography. Our results strongly suggest the role of human GSTs in the modulation of odorant availability to ORs in the peripheral olfactory process.
Subject(s)
Glutathione Transferase/metabolism , Odorants , Olfactory Mucosa/metabolism , Glutathione Transferase/analysis , HumansABSTRACT
The detection and processing of chemical stimuli involve coordinated neuronal networks that process sensory information. This allows animals, such as the model species Drosophila melanogaster, to detect food sources and to choose a potential mate. In peripheral olfactory tissues, several classes of proteins are acting to modulate the detection of chemosensory signals. This includes odorant-binding proteins together with odorant-degrading enzymes (ODEs). These enzymes, which primarily act to eliminate toxic compounds from the whole organism also modulate chemodetection. ODEs are thought to neutralize the stimulus molecule concurrently to its detection, avoiding receptor saturation thus allowing chemosensory neurons to respond to the next stimulus. Here, we show that one UDP-glycosyltransferase (UGT36E1) expressed in D. melanogaster antennal olfactory sensory neurons (OSNs) is involved in sex pheromone discrimination. UGT36E1 overexpression caused by an insertion mutation affected male behavioral ability to discriminate sex pheromones while it increased OSN electrophysiological activity to male pheromones. Reciprocally, the decreased expression of UGT36E1, controlled by an RNAi transgene, improved male ability to discriminate sex pheromones whereas it decreased electrophysiological activity in the relevant OSNs. When we combined the two genotypes (mutation and RNAi), we restored wild-type-like levels both for the behavioral discrimination and UGT36E1 expression. Taken together, our results strongly suggest that this UGT plays a pivotal role in Drosophila pheromonal detection.
Subject(s)
Drosophila Proteins/genetics , Drosophila melanogaster/genetics , Glycosyltransferases/genetics , Pheromones/genetics , Sex Attractants/genetics , Smell/genetics , Animals , Animals, Genetically Modified/genetics , Drosophila melanogaster/physiology , Female , Male , Odorants/analysis , Olfactory Bulb/metabolism , Olfactory Receptor Neurons , Sensation/genetics , Sexual Behavior, AnimalABSTRACT
Resveratrol has been proposed to prevent tumor growth and the different steps of carcinogenesis; nevertheless, these biological effects are sometimes discordant between different cell types. Several hypotheses and works have suggested that the metabolism of resveratrol could be at the origin of a different cellular response. We show here, using colorectal tumor cell lines, that the biological effects of RSV result mainly from its carriage by carriers of the superfamily of ABC transporter, i.e., P-gP, MRP, or BCRP. Using cell lines overexpressing these different transporters, we have been able to highlight the importance of P-gP in the response of cells to RSV. These results were confirmed by invalidating the gene coding for P-gP, which restored the sensitivity of colorectal cells resistant to the polyphenol. Subsequently, the status of P-glycoprotein expression is an important element to be taken into consideration in the cytotoxic activity of resveratrol in colorectal cancer cells.
Subject(s)
ATP Binding Cassette Transporter, Subfamily B, Member 1/metabolism , Colorectal Neoplasms/drug therapy , Enzyme Inhibitors/pharmacology , Resveratrol/pharmacology , ATP Binding Cassette Transporter, Subfamily B/genetics , ATP Binding Cassette Transporter, Subfamily B/metabolism , ATP-Binding Cassette Transporters/metabolism , Apoptosis/drug effects , Cell Line, Tumor , Cell Survival/drug effects , Colorectal Neoplasms/metabolism , Drug Resistance, Neoplasm , Enzyme Inhibitors/metabolism , Gene Expression Regulation, Neoplastic/drug effects , Gene Silencing , Humans , Resveratrol/metabolismABSTRACT
The olfactory epithelium is continuously exposed to exogenous chemicals, including odorants. During the past decade, the enzymes surrounding the olfactory receptors have been shown to make an important contribution to the process of olfaction. Mammalian xenobiotic metabolizing enzymes, such as cytochrome P450, esterases and glutathione transferases (GSTs), have been shown to participate in odorant clearance from the olfactory receptor environment, consequently contributing to the maintenance of sensitivity toward odorants. GSTs have previously been shown to be involved in numerous physiological processes, including detoxification, steroid hormone biosynthesis, and amino acid catabolism. These enzymes ensure either the capture or the glutathione conjugation of a large number of ligands. Using a multi-technique approach (proteomic, immunocytochemistry and activity assays), our results indicate that GSTs play an important role in the rat olfactory process. First, proteomic analysis demonstrated the presence of different putative odorant metabolizing enzymes, including different GSTs, in the rat nasal mucus. Second, GST expression was investigated in situ in rat olfactory tissues using immunohistochemical methods. Third, the activity of the main GST (GSTM2) odorant was studied with in vitro experiments. Recombinant GSTM2 was used to screen a set of odorants and characterize the nature of its interaction with the odorants. Our results support a significant role of GSTs in the modulation of odorant availability for receptors in the peripheral olfactory process.