Receptors carbohydrates

Rouiller DG, Sharon N, McElduff A, Podskalny JM, Gorden P 1986 Lectins as probes of insulin receptor carbohydrate composition studies in glycosylation mutants of Chinese hamster ovarian cells with altered insulin binding. Endocrinology 118 1159-1165... 

Receptors carbohydrates may also serve as specific membrane receptors for extracellular substances such as hormones. 

J. Lehmann and U. P. Weitzel, Synthesis and application of a-D-mannosyl clusters as photoaffinity ligands for mannose-binding proteins Concanavalin A as a model receptor, Carbohydr. Res., 294 (1996) 65-94. 

Owing to the weakness of carbohydrate receptor-protein interactions, in order to attain biological meaningful affinities for the receptor, carbohydrates very often need to be clustered and expressed in multiple copies. For this purpose glycodendrimers, which are multivalent glycoconjugates with well-defined chemical structures, have received recent attention for their considerable potential as tools for studying cell-surface protein-carbohydrate interactions, because of the affinity enhancement obtained by multivalency. 

Monovalent and multivalent fluorescent probes can be utilized to evaluate the influence of oligosaccharide clustering on recognition by cell-surface lectins. Fluorescence microscopy and flow cytometry are appropriate methods to visualize the corresponding receptor-carbohydrate interactions. 

Enzymatic synthesis of dimeric glycomimetic ligands of NK cell activation receptors. Carbohydr. Res., 346,... 

Fig. 4. Representation of proposed topography of human oxytocin receptor (85) where CHO represents carbohydrate.

An alternative view (123) is that no single model can adequately explain why any given compound is sweet. This hypothesis derives from several features. First, there is the observation that all carbohydrates having a critical ratio of OH to C are sweet tasting. In other words, there are no stmctural constraints to the sweetness of carbohydrates. Second, not all sweeteners can be fit to the same SAR model. Rather, some fit one, others fit another. Third, studies on the transduction mechanisms of sweetness suggest more than a single mechanism for sweet taste, implying multiple receptors for sweeteners. 

In addition to binding to sialic acid residues of the carbohydrate side chains of cellular proteins that the virus exploits as receptors, hemagglutinin has a second function in the infection of host cells. Viruses, bound to the plasma membrane via their membrane receptors, are taken into the cells by endocytosis. Proton pumps in the membrane of endocytic vesicles that now contain the bound viruses cause an accumulation of protons and a consequent lowering of the pH inside the vesicles. The acidic pH (below pH 6) allows hemagglutinin to fulfill its second role, namely, to act as a membrane fusogen by inducing the fusion of the viral envelope membrane with the membrane of the endosome. This expels the viral RNA into the cytoplasm, where it can begin to replicate. 

Many proteins found in nature are glycoproteins because they contain covalently linked oligo- and polysaccharide groups. The list of known glycoproteins includes structural proteins, enzymes, membrane receptors, transport proteins, and immunoglobulins, among others. In most cases, the precise function of the bound carbohydrate moiety is not understood. 

The first hormonal signal found to comply with the characteristics of both a satiety and an adiposity signal was insulin [1]. Insulin levels reflect substrate (carbohydrate) intake and stores, as they rise with blood glucose levels and fall with starvation. In addition, they may reflect the size of adipose stores, because a fatter person secretes more insulin than a lean individual in response to a given increase of blood glucose. This increased insulin secretion in obesity can be explained by the reduced insulin sensitivity of liver, muscle, and adipose tissue. Insulin is known to enter the brain, and direct administration of insulin to the brain reduces food intake. The adipostatic role of insulin is supported by the observation that mutant mice lacking the neuronal insulin receptor (NDRKO mice) develop obesity. 

Triiodothyronine (3, 5,3-L-triiodothyronine, T3) is a thyroid hormone. It is producedby outer ring deiodination of thyroxine (T4) in peripheral tissues. The biologic activity of T3 is 3-8 times higher than that of T4. T3 is 99.7% protein-bound and is effective in its free non-protein-bound form. The half-life of triiodothyronine is about 19 h. The daily tur nover of T3 is 75%. Triiodothyronine acts via nuclear receptor binding with subsequent induction of protein synthesis. Effects of thyroid hormones are apparent in almost all organ systems. They include effects on the basal metabolic rate and the metabolisms of proteins, lipids and carbohydrates. 

Jacques V, Desreux JF (2002) New Classes of MRI Contrast Agents. 221 123-164 James TD, Shinkai S (2002) Artificial Receptors as Chemosensors for Carbohydrates. 218 159-200... 

James TD, Shinkai S (2002) Artificial Receptors as Chemosensors for Carbohydrates. 218 ... 

C-type lectins Characterized by a Ca +-dependent carbohydrate recognition domain (CRD) includes the mammalian asialoglycoprotein receptor, the selectins, and the mannosebinding protein... 

Glycophorin A appears to serve a variety of functions on the red-cell membrane, and has been implicated in several red-cell disorders. Because it extends from the external environment of the cell into the cell cytoplasm, it is considered to constitute a receptor for malarial parasites,"" influenza viruses, lectins, and Portuguese man-of-war toxin. Many of these receptor functions are attributable to the carbohydrate composition of these... 

That the sweet and bitter responses are intimately associated is clear from the results of gustatory studies of all of the conformationally defined sugars and of other organic compounds. If a carbohydrate has any taste at all, this is invariably sweet, bitter-sweet, or bitter. Chemical modification may alter the taste of a sweet compound so that the product is bitter-sweet or bitter, and it is now generally agreed that the two basic tastes may each be a feature of a single compound. It appears, therefore, that the interactions of these polyfunctional stimulants involve two different sets of receptor sites, representing sweet and bitter modalities. ... 

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