昆虫化学感受蛋白

化学感受蛋白(chemosensory proteins,CSPs)是广泛存在于各种昆虫的疏水性蛋白,被认为在昆虫嗅觉行为中执行了运载非挥发性气味分子到达相应受体的功能。文章从序列特征、二级和三维结构、结合配体、表达特征、生理功能和进化地位等方面进行较详细的介绍,并从理论和实践角度探讨CSPs的研究前景和重点。     

Cloning, Pharmacology, and Tissue Distribution of G-Protein-Coupled Receptor GPR105 (KIAA0001) Rodent Orthologs

It has recently been shown that UDP-glucose is a potent agonist of the orphan G-protein-coupled receptor (GPCR) KIAA0001. Here we report cloning and analysis of the rat and mouse orthologs of this receptor. In accordance with GPCR nomenclature, we have renamed the cDNA clone, KIAA0001, and its orthologs GPR105 to reflect their functionality as G-protein-coupled receptors. The rat and mouse orthologs show 80% and 83% amino acid identity, respectively, to the human GPR105 protein. We demonstrate by genomic Southern blot analysis that there are no genes in the mouse or rat genomes with higher sequence similarity. Chromosomal mapping shows that the mouse and human genes are located on syntenic regions of chromosome 3. Further analyses of the rat and mouse GPR105 proteins show that they are activated by the same agonists as the human receptor, responding to UDP-glucose and closely related molecules with similar affinities. The mouse and rat receptors are widely expressed, as is the human receptor. Thus we conclude that we have identified the rat and mouse orthologs of the human gene GPR105.     

Targeting of two signal transduction pathways to different regions of the bacterial cell

Components of bacterial chemosensory pathways which sense via transmembrane receptors have been shown to localize to the cell poles. Many species, however, have operons encoding multiple putative chemosensory pathways, some including putative cytoplasmic receptors. In-genome fusions to single or multiple genes encoding components of two chemosensory pathways in Rhodobacter sphaeroides, cheOp2 and cheOp3, revealed that while sensory transducing proteins associated with transmembrane receptors and encoded on cheOp2 were targeted to the cell poles, the proteins associated with putative cytoplasmic receptors and encoded on cheOp3 were all targeted to a cytoplasmic cluster. No proteins were localized to both sites. These data show that bacteria target components of related pathways to different sites in the cell, presumably preventing direct cross-talk between the different pathways, but allowing a balanced response between extracellular and cytoplasmic signals. It also indicates that there is intracellular organization in bacterial cells, with specific proteins targeted and localized to cytoplasmic regions.     

The sea lamprey Petromyzon marinus genome reveals the early origin of several chemosensory receptor families in the vertebrate lineage

Background  

In gnathostomes, chemosensory receptors (CR) expressed in olfactory epithelia are encoded by evolutionarily dynamic gene families encoding odorant receptors (OR), trace amine-associated receptors (TAAR), V1Rs and V2Rs. A limited number of OR-like sequences have been found in invertebrate chordate genomes. Whether these gene families arose in basal or advanced vertebrates has not been resolved because these families have not been examined systematically in agnathan genomes.     

Chemosensory signaling in C. elegans

The nematode Caenorhabditis elegans can sense and respond to hundreds of different chemicals with a simple nervous system, making it an excellent model for studies of chemosensation. The chemosensory neurons that mediate responses to different chemicals have been identified through laser ablation studies, providing a cellular context for chemosensory signaling. Genetic and molecular analyses indicate that chemosensation in nematodes involves G protein signaling pathways, as it does in vertebrates, but the receptors and G proteins involved belong to nematode-specific gene families. It is likely that about 500 different chemosensory receptors are used to detect the large spectrum of chemicals to which C. elegans responds, and one of these receptors has been matched with its odorant ligand. C. elegans olfactory responses are also subject to regulation based on experience, allowing the nematode to respond to a complex and changing chemical environment.     

G-protein-coupled receptors in intestinal chemosensation

Food intake is detected by the chemical senses of taste and smell and subsequently by chemosensory cells?in the gastrointestinal tract that link the composition of ingested foods to feedback circuits controlling gut motility/secretion, appetite, and peripheral nutrient disposal. G-protein-coupled receptors responsive to?a range of nutrients and other food components have been identified, and many are localized to intestinal chemosensory cells, eliciting hormonal and neuronal signaling to the brain and periphery. This review examines the role of G-protein-coupled receptors as signaling molecules in the gut, with a particular focus on pathways relevant to appetite and glucose homeostasis.     

Afferent modulation of dopamine neuron firing patterns

In recent studies examining the modulation of dopamine (DA) cell firing patterns, particular emphasis has been placed on excitatory afferents from the prefrontal cortex and the subthalamic nucleus. A number of inconsistencies in recently published reports, however, do not support the contention that tonic activation of NMDA receptors is the sole determinate of DA neuronal firing patterns. The results of work on the basic mechanism of DA firing and the action of apamin suggest that excitatory projections to DA neurons from cholinergic and glutamatergic neurons in the tegmental pedunculopontine nucleus, and/or inhibitory GABAergic projections, are also involved in modulating DA neuron firing behavior.     

Review: Chemosensing of nutrients and non-nutrients in the human and porcine gastrointestinal tract

The gastrointestinal tract (GIT) is an interface between the external and internal milieus that requires continuous monitoring for nutrients or pathogens and toxic chemicals. The study of the physiological/molecular mechanisms, mediating the responses to the monitoring of the GIT contents, has been referred to as chemosensory science. While most of the progress in this area of research has been obtained in laboratory rodents and humans, significant steps forward have also been reported in pigs. The objective of this review was to update the current knowledge on nutrient chemosensing in pigs in light of recent advances in humans and laboratory rodents. A second objective relates to informing the existence of nutrient sensors with their functionality, particularly linked to the gut peptides relevant to the onset/offset of appetite. Several cell types of the intestinal epithelium such as Paneth, goblet, tuft and enteroendocrine cells (EECs) contain subsets of chemosensory receptors also found on the tongue as part of the taste system. In particular, EECs show specific co-expression patterns between nutrient sensors and/or transceptors (transport proteins with sensing functions) and anorexigenic hormones such as cholecystokinin (CCK), peptide tyrosine tyrosine (PYY) or glucagon-like peptide-1 (GLP-1), amongst others. In addition, the administration of bitter compounds has an inhibitory effect on GIT motility and on appetite through GLP-1-, CCK-, ghrelin- and PYY-labelled EECs in the human small intestine and colon. Furthermore, the mammalian chemosensory system is the target of some bacterial metabolites. Recent studies on the human microbiome have discovered that commensal bacteria have developed strategies to stimulate chemosensory receptors and trigger host cellular functions. Finally, the study of gene polymorphisms related to nutrient sensors explains differences in food choices, food intake and appetite between individuals.     

Solution structure of a chemosensory protein from the desert locust Schistocerca gregaria

Chemical stimuli, generally constituted by small volatile organic molecules, are extremely important for the survival of different insect species. In the course of evolution, insects have developed very sophisticated biochemical systems for the binding and the delivery of specific semiochemicals to their cognate membrane-bound receptors. Chemosensory proteins (CSPs) are a class of small soluble proteins present at high concentration in insect chemosensory organs; they are supposed to be involved in carrying the chemical messages from the environment to the chemosensory receptors. In this paper, we report on the solution structure of CSPsg4, a chemosensory protein from the desert locust Schistocerca gregaria, which is expressed in the antennae and other chemosensory organs. The 3D NMR structure revealed an overall fold consisting of six alpha-helices, spanning residues 13-18, 20-31, 40-54, 62-78, 80-90, and 97-103, connected by loops which in some cases show dihedral angles typical of beta-turns. As in the only other chemosensory protein whose structure has been solved so far, namely, CSP from the moth Mamestra brassicae, four helices are arranged to form a V-shaped motif; another helix runs across the two V's, and the last one is packed against the external face. Analysis of the tertiary structure evidenced multiple hydrophobic cavities which could be involved in ligand binding. In fact, incubation of the protein with a natural ligand, namely, oleamide, produced substantial changes to the NMR spectra, suggesting extensive conformational transitions upon ligand binding.     

T1R3 is expressed in brush cells and ghrelin-producing cells of murine stomach

Various digestive and enteroendocrine signaling processes are constantly being adapted to the chemical composition and quantity of the chyme contained in the diverse compartments of the gastrointestinal tract. The chemosensory monitoring that underlies the adaptive capacity of the gut is thought to be performed by so-called brush cells that share morphological and molecular features with gustatory sensory cells. A substantial population of brush cells is localized in the gastric mucosa. However, no chemosensory receptors have been found to be expressed in these cells so far, challenging the concept that they serve a chemosensory function. The canonical chemoreceptors for the detection of macronutrients are taste receptors belonging to the T1R family; these have been identified in several tissues in addition to the gustatory system including the small intestine. We demonstrate the expression of the T1R subtype T1R3, which is essential for the detection of both sugars and amino acids in the gustatory system, in two distinct cell populations of the gastric mucosa. One population corresponds to open-type brush cells, emphasizing the notion that they are a chemosensory cell type; T1R3 immunoreactivity in these cells is restricted to the apical cell pole, which might provide the basis for the detection of luminal macronutrient compounds. The second gastric T1R3-positive population consists of closed-type endocrine cells that produce ghrelin. This finding suggests that ghrelin-releasing cells, which lack access to the stomach lumen, might receive chemosensory input from macronutrients in the circulation via T1R3.     

The modality of the dominance signal in snapping shrimp (Alpheus heterochaelis) and the corresponding setal types on the antennules

Previous behavioural experiments showed that snapping shrimp lacking lateral antennular filaments, i.e. without chemosensory aesthetascs, lose the ability to distinguish between conspecifics that are inexperienced in fighting and former winners. A chemosensory dominance signal was assumed to be present, although other receptors unique to the lateral filaments may have been responsible for the behavioural changes. In the present study, the antennules of snapping shrimp were examined for differences between the lateral and medial antennule filaments to identify the modality of the dominance signal. We found six different types of setae and two types of pores. A new probably bimodal setal type is described, the broad long simple seta. Only the chemosensory aesthetascs and their associated hydrosensory companion setae are unique to the lateral filament. Thus we conclude that the dominance signal is chemical, because a hydrodynamic signal would be also received by the simple setae distributed on both filaments.     

The modality of the dominance signal in snapping shrimp (Alpheus heterochaelis) and the corresponding setal types on the antennules

Previous behavioural experiments showed that snapping shrimp lacking lateral antennular filaments, i.e. without chemosensory aesthetascs, lose the ability to distinguish between conspecifics that are inexperienced in fighting and former winners. A chemosensory dominance signal was assumed to be present, although other receptors unique to the lateral filaments may have been responsible for the behavioural changes. In the present study, the antennules of snapping shrimp were examined for differences between the lateral and medial antennule filaments to identify the modality of the dominance signal. We found six different types of setae and two types of pores. A new probably bimodal setal type is described, the broad long simple seta. Only the chemosensory aesthetascs and their associated hydrosensory companion setae are unique to the lateral filament. Thus we conclude that the dominance signal is chemical, because a hydrodynamic signal would be also received by the simple setae distributed on both filaments.     

Hypothalamic control of feeding

Our understanding of the hypothalamic control of energy homeostasis has increased greatly since the discovery of leptin, the adipose cell derived protein. Recent studies have identified several new hypothalamic neuropeptides that affect food intake and energy balance. By studying these molecules and their neuronal systems, receptors and interactions, we are beginning to unravel the circuitry between peripheral adipogenic signals and hypothalamic effector pathways.     

Recent structural advances in bacterial chemotaxis signalling

Bacterial chemosensory arrays have served as a model system for in-situ structure determination, clearly cataloguing the improvement of cryo-electron tomography (cryoET) over the past decade. In recent years, this has culminated in an accurately fitted atomistic model for the full-length core signalling unit (CSU) and numerous insights into the function of the transmembrane receptors responsible for signal transduction. Here, we review the achievements of the latest structural advances in bacterial chemosensory arrays and the developments which have made such advances possible.     

Shared and unique G alpha proteins in the zebrafish versus mammalian senses of taste and smell

Chemosensory systems in vertebrates employ G protein-coupled receptors as sensors. In mammals, several families of olfactory and gustatory receptors as well as specific G alpha proteins coupling to them have been identified, for example, gustducin for taste. Orthologous receptor families have been characterized in fish, but the corresponding G alpha genes have not been well investigated so far. We have performed a comprehensive search of several lower vertebrate genomes to establish the G alpha protein family in these taxa and to identify those genes that may be involved in chemosensory signal transduction in fish. We report that gustducin is absent from the genomes of all teleost and amphibian species analyzed, presumably due to independent gene losses in these lineages. However, 2 other G alpha genes, Gi1b and G14a, are expressed in zebrafish taste buds and 4 G proteins, Go1, Go2, Gi1b, and Golf2, were detected in the olfactory epithelium. Golf2, Gi1b, and G14a are expressed already shortly after hatching, consistent with the physiological and behavioral responses of larvae to odorants and tastants. Our results show general similarity to the mammalian situation but also clear-cut differences and as such are essential for using the zebrafish model system to study chemosensory perception.     

The pharmacology and signaling of bitter, sweet, and umami taste sensing

Over the last decade, many of the molecular components that mediate the transduction of taste signaling have been elucidated. The chemosensory receptors for taste have been identified as G protein-coupled receptors (GPCRs) and ion channels that are expressed on the surface of highly specialized taste sensory cells. Tastant molecules act as agonists, binding to and stabilizing active conformations of receptors, resulting in the initiation of signal transduction cascades. Taste signaling, therefore, should be amenable to the methods of pharmacology. This review focuses on the GPCR-mediated signaling of bitter, sweet, and umami tastes and emphasizes the opportunities for pharmacologic evaluation.     

Nucleotide Sequence, Genomic Organization, and Chromosomal Localization of Genes Encoding the Human NMDA Receptor Subunits NR3A and NR3B

The N-methyl-D-aspartate (NMDA) receptors are glutamate-regulated ion channels that are critically involved in important physiological and pathological functions of the mammalian central nervous system. We have identified and characterized the gene encoding the human NMDA receptor subunit NR3A (GRIN3A), as well as the gene (GRIN3B) encoding an entirely novel subunit that we named NR3B, as it is most closely related to NR3A (57.4% identity). GRIN3A localizes to chromosome 9q34, in the region 13-34, and consists of nine coding exons. The deduced protein contains 1115 amino acids and shows 92.7% identity to rat NR3A. GRIN3B localizes to chromosome 19p13.3 and contains, as does the mouse NR3B gene (Grin3b), eight coding exons. The deduced proteins of human and mouse NR3B contain 901 and 900 amino acid residues, respectively (81.6% identity). In situ hybridization shows a widespread distribution of Grin3b mRNA in the brain of the adult rat.     

Olfactory receptors in Bactrocera species for sustainable fruit fly management: A review and future perspectives

Molecular studies on odorant receptors (ORs), odorant-binding proteins (OBPs) and the functioning of the receptor and pheromone signal transduction in fruit fly Bactrocera species have expanded exponentially during the past few decades. OBPs contribute to the sensing of the olfactory system (OS) via the transduction of odorants through the sensillum lymph. However, ORs, a family of G-protein-coupled receptors in Bactrocera and various other species, exhibit heightened responsiveness to multiple chemical odours such as hormones, sensory stimuli and neurotransmitters. The apparent mechanism involves a combinatorial code encompassing both peripheral and antennal lobe processing, facilitating the reception of sexual pheromones and environmental cues. The OS is specifically designed to recognize and process information from volatile chemical signals, and these chemical signals play an important function in various flies. Insects rely on these chemicals to navigate and comprehend their surroundings. A mature insect OS is composed of two pairs of sensillae-covered palps, antennae and two primary pairs of olfactory appendages on the anterior head. It has been shown that chemosensory gene families contribute in odour perception. These include various neuroreceptor families, such as OBPs, chemosensory proteins and sensory neuron membrane proteins. Additionally, there are three divergent chemoreceptors, namely ORs, ionotropic receptors and gustatory receptors. Methods based on systematic biology, molecular biology and bioinformatics tools have rapidly emerged to investigate the insect communication systems and provide new insights for the management of many agricultural pest. Several aromatic compounds, including semiochemicals and pheromones, have been employed to defend crops and animals from destructive fruit flies and other invasive and frugivorous species. To promote the expansion of the cropping system, the utilization of phytochemical lures can be convenient for sustainable agriculture production and enhance food security. Hence, this review examined the state of the art in chemical communication of insects with a focus on fruit fly pest species to identify OS and their semiochemical receptors, protein receptors and chemosensory receptors (CSRs), as well as their practical applications for biological control and integrated pest management are highlighted.