Molecular structure and conformation in taste perception

Master of ScienceFisheriesUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/114377/1/39015003264754.pd

Stimulation of the gerbil's gustatory receptors by disaccharides

The gustatory responses from the chorda tympani nerve of the Mongolian gerbil, Meriones unguiculatus, were with 13 disaccharides. Sucrose was the most stimulatory sugar.The ability of fructosyl glycosides to stimulate amy depend upon the linkage between fructose and the glycoside. Disaccharides possessing 1 --> 3, 1 --> 4, or 1 --> 6 linkages were poor stimuli compared to sucrose which has a 1 --> 2 linkage. Glucopyranosyl disaccharides with an [alpha]-linkage were better stimuli than [beta]-anomers, while galactopyranosyl disaccharides possessing a [beta]-linkage were better than their [alpha]-anomers.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/21721/1/0000113.pd

Stimulation of the gerbil's gustatory receptors by polyols

The gustatory responses of the Mongolian gerbil were tested with 12 sugar alcohols. The electrophysiological effectiveness of the linear polyols as gustatory stimulants increased as the length of the carbon chain increased from 2 to 5. Six and 7 carbon acyclic polyols were no more effective than the pentitols. By comparison myoinositol, a cyclic polyol, was more effective in evoking a response. Responses to mixtures of -sorbitol and sucrose suggest that these sugars compete for a common receptor site. A sucrose receptor site and a model of it is proposed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/21723/1/0000115.pd

Stimulation of the gerbil's gustatory receptors by monosaccharides

The gustatory responses of the Mongolian gerbil were tested with a large number of monosaccharides. Electrophysiological methods were used to record from the chorda tympani nerve. Methyl glycosides which have structural features in common with sucrose are the most effective monosaccharides for eliciting a neural response. Among the monosaccharides tested, efficacy appears to be highest in -pyranosides having equatorial substituents at the C-2 and C-4 positions and axial substituents at the C-1 position. A C-5 hydroxymethyl group is not required. Similarities in the structural requirements for taste response in the fly and gerbil are discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/21722/1/0000114.pd

Taste fiber responses during reinnervation of fungiform papillae

Crushing or transecting the chorda tympani nerve of the gerbil ( Meriones unguiculatus ) caused ipsilateral degeneration of taste buds in the fungiform papillae. In less than two weeks some taste fibers regenerated into the tongue and formed new taste buds and receptor cells. The recovery process was evaluated electrophysiologically in 53 gerbils by acute recording proximal to the nerve injury site. Initially the chorda tympani was electrically silent. In gerbils tested at later times spontaneous activity appeared. This was followed by responses to pressure on the tongue. Taste responses returned as early as dasy 11. The receptive field of regenerated taste fibers was limited to a small number of fungiform papillae. Taste responses were always associasted with the presence of one or more taste buds in the receptive field. Taste buds identified as responsive to chemicals contained some fusiform cells. We found thast the taste responses of single fiber, few-fiber and multi-unit preparations reflected the diversity of responses found in normal taste axons as determined by recording from 26 normal single fibers and 27 normal whole nerves. The early emergence of a variety of fiber types and responses to many chemicals in regeneration is inconsistent with the proposition that the relative chemical responsiveness of a receptor cell is strictly a function of its age; the response of a given young taste receptor is not necessarily limited to a few of the standard taste stimulants.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/49998/1/901720406_ftp.pd

Sugar receptor specificity in the fleshfly, Sarcophaga bullata

Various carbohydrates were tested for stimulating activity of the sweet receptor of Sarcophaga bullata. Efficacy appears to be highest in -pyranosides having equatorial substituents at C-2, C-3, C-4 and C-5, with the exception of the C-1 position where equatorial substituents detract. Similarly, myo-inositol, having 5 equatorial and 1 axial hydroxyl, is the most stimulatory of the cyclitols tested. The anomalous action of several compounds remains unexplained. -Glucose is stimulatory, while its [alpha]- and [beta]-pyranosides are not. Similarly, free fructose, an extremely potent sugar, is completely inactive as its [alpha]- or [beta]-furanoside or its [alpha]- or [beta]-pyranoside. This finding is discussed in relation to the stimulatory action of sucrose.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/33504/1/0000001.pd

The stereospecificity of the inositol receptor of the silkworm Bombyx mori

The specificity of the `sugar-sensitive' hair (Ss-I) in the silkworm to the 9 isomers of myo-inositol was studied electrophysiologically. Of the 9 isomers only myo-, epi- and allo-inositol receptor activity. Using various mixtures of these cyclitols and sucrose it was determined that the inositol receptor located in the Ss-I hair responded only to myo- and epi-inositol while allo-inositol stimulated another receptor in the same hair. Threshold and magnitude of response of this receptor were nearly the same for both cyclitols. Configurational specificity of the inositol receptor and its role in taste and lipid metabolism are discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/33549/1/0000049.pd

An efficient approach to finding Siraitia grosvenorii triterpene biosynthetic genes by RNA-seq and digital gene expression analysis

<p>Abstract</p> <p>Background</p> <p><it>Siraitia grosvenorii </it>(Luohanguo) is an herbaceous perennial plant native to southern China and most prevalent in Guilin city. Its fruit contains a sweet, fleshy, edible pulp that is widely used in traditional Chinese medicine. The major bioactive constituents in the fruit extract are the cucurbitane-type triterpene saponins known as mogrosides. Among them, mogroside V is nearly 300 times sweeter than sucrose. However, little is known about mogrosides biosynthesis in <it>S. grosvenorii</it>, especially the late steps of the pathway.</p> <p>Results</p> <p>In this study, a cDNA library generated from of equal amount of RNA taken from <it>S. grosvenorii </it>fruit at 50 days after flowering (DAF) and 70 DAF were sequenced using Illumina/Solexa platform. More than 48,755,516 high-quality reads from a cDNA library were generated that was assembled into 43,891 unigenes. De novo assembly and gap-filling generated 43,891 unigenes with an average sequence length of 668 base pairs. A total of 26,308 (59.9%) unique sequences were annotated and 11,476 of the unique sequences were assigned to specific metabolic pathways by the Kyoto Encyclopedia of Genes and Genomes. cDNA sequences for all of the known enzymes involved in mogrosides backbone synthesis were identified from our library. Additionally, a total of eighty-five cytochrome P450 (CYP450) and ninety UDP-glucosyltransferase (UDPG) unigenes were identified, some of which appear to encode enzymes responsible for the conversion of the mogroside backbone into the various mogrosides. Digital gene expression profile (DGE) analysis using Solexa sequencing was performed on three important stages of fruit development, and based on their expression pattern, seven <it>CYP450</it>s and five <it>UDPG</it>s were selected as the candidates most likely to be involved in mogrosides biosynthesis.</p> <p>Conclusion</p> <p>A combination of RNA-seq and DGE analysis based on the next generation sequencing technology was shown to be a powerful method for identifying candidate genes encoding enzymes responsible for the biosynthesis of novel secondary metabolites in a non-model plant. Seven <it>CYP450</it>s and five <it>UDPG</it>s were selected as potential candidates involved in mogrosides biosynthesis. The transcriptome data from this study provides an important resource for understanding the formation of major bioactive constituents in the fruit extract from <it>S. grosvenorii</it>.</p

Comparative gustatory responses in four species of gerbilline rodents

Integrated taste responses to chemical stimulation of the tongue were recorded from the intact chorda tympani nerve in four species of gerbils ( Meriones libycus, M. shawi, M. unguiculatus and Psammomys obesus ).Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47116/1/359_2004_Article_BF00618177.pd

Topological and Functional Characterization of an Insect Gustatory Receptor

Insect gustatory receptors are predicted to have a seven-transmembrane structure and are distantly related to insect olfactory receptors, which have an inverted topology compared with G-protein coupled receptors, including mammalian olfactory receptors. In contrast, the topology of insect gustatory receptors remains unknown. Except for a few examples from Drosophila, the specificity of individual insect gustatory receptors is also unknown. In this study, the total number of identified gustatory receptors in Bombyx mori was expanded from 65 to 69. BmGr8, a silkmoth gustatory receptor from the sugar receptor subfamily, was expressed in insect cells. Membrane topology studies on BmGr8 indicate that, like insect olfactory receptors, it has an inverted topology relative to G protein-coupled receptors. An orphan GR from the bitter receptor family, BmGr53, yielded similar results. We infer, from the finding that two distantly related BmGrs have an intracellular N-terminus and an odd number of transmembrane spans, that this is likely to be a general topology for all insect gustatory receptors. We also show that BmGr8 functions independently in Sf9 cells and responds in a concentration-dependent manner to the polyalcohols myo-inositol and epi-inositol but not to a range of mono- and di-saccharides. BmGr8 is the first chemoreceptor shown to respond specifically to inositol, an important or essential nutrient for some Lepidoptera. The selectivity of BmGr8 responses is consistent with the known responses of one of the gustatory receptor neurons in the lateral styloconic sensilla of B. mori, which responds to myo-inositol and epi-inositol but not to allo-inositol