About: Sialic acid is a(n) research topic. Over the lifetime, 10929 publication(s) have been published within this topic receiving 414624 citation(s). The topic is also known as: (4S,5R,6R,7S,8R)-5-acetamido-4,6,7,8,9-pentahydroxy-2-oxononanoic acid & sialic acid.
01 Aug 1959-Journal of Biological Chemistry
TL;DR: This chapter discusses the different aspects of thiobarbituric acid assay of sialic acid, which is suitable for measuring the release of bound sialoic acid by sialidase and hydrolysis of sIALic acid-containing material must be carried out for the measurement of total sialsic acids.
Abstract: Publisher Summary This chapter discusses the different aspects of thiobarbituric acid assay of sialic acid. Periodate oxidation of the neuraminic acid backbone of sialic acids results in the formation of β -formylpyruvic acid from carbon atoms 1 to 4. The N -acetyl or N -glycolyl group of sialic acids apparently does not interfere with periodate oxidation. β -Formylpyruvic acid is coupled with 2-thiobarbituric acid to form a red chromophore with a maximum absorption at 549 mμ. It is found that as only free sialic acids are reactive in the assay, hydrolysis of sialic acid-containing material must be carried out for the measurement of total sialic acids. The assay is suitable for measuring the release of bound sialic acid by sialidase. A series of 2-keto, 3-deoxy sugar acids, found in bacteria, also react in the thiobarbituric acid assay. These produce a chromogen with a peak at 549 mμ. They can be readily distinguished from sialic acids because they are not reactive in the orcinol or direct Ehrlich assays for sialic acids. The hydrolysis frees all the sialic acids from several mucoproteins that have been tested except for brain tissue where release of sialic acids takes place for several hours.
01 Jan 1957-Biochimica et Biophysica Acta
TL;DR: A new method for the quantitive determination of sialic acids is described, which is about 50% more sensitive than the orcinol-hydrochloric acid method generally used and considerably lower with the resorcin reagent.
Abstract: A new method for the quantitive determination of sialic acids is described. Optimal conditions for the colour formation were investigated. The molar absorbancy indices of N-acetylsialic acid, N-glycolysialic and N, O-diacetylsialic acid and several naturally-occuringg carbohydrates were determined. The method is about 50% more sensitive than the orcinol-hydrochloric acid method generally used. The influence of other carbohydrates is also considerably lower with the resorcin reagent. The recovery of N-acetylsialic acid from known mixtures with galactose and fructose was determined. The detemination of sialic acid in body fluid proteins is briefly discussed.
01 Jan 2000-Annual Review of Biochemistry
TL;DR: Comparisons to the soluble N-ethyl-maleimide-sensitive factor attachment protein receptor (SNARE) protein complex of vesicle fusion suggests that these molecules are all in the fusion-activated conformation and that the juxtaposition of the membrane anchor and fusion peptide, a recurring feature, is involved in the fused mechanism.
Abstract: Hemagglutinin (HA) is the receptor-binding and membrane fusion glycoprotein of influenza virus and the target for infectivity-neutralizing antibodies. The structures of three conformations of the ectodomain of the 1968 Hong Kong influenza virus HA have been determined by X-ray crystallography: the single-chain precursor, HA0; the metastable neutral-pH conformation found on virus, and the fusion pH-induced conformation. These structures provide a framework for designing and interpreting the results of experiments on the activity of HA in receptor binding, the generation of emerging and reemerging epidemics, and membrane fusion during viral entry. Structures of HA in complex with sialic acid receptor analogs, together with binding experiments, provide details of these low-affinity interactions in terms of the sialic acid substituents recognized and the HA residues involved in recognition. Neutralizing antibody-binding sites surround the receptor-binding pocket on the membrane-distal surface of HA, and the structures of the complexes between neutralizing monoclonal Fabs and HA indicate possible neutralization mechanisms. Cleavage of the biosynthetic precursor HA0 at a prominent loop in its structure primes HA for subsequent activation of membrane fusion at endosomal pH (Figure 1). Priming involves insertion of the fusion peptide into a charged pocket in the precursor; activation requires its extrusion towards the fusion target membrane, as the N terminus of a newly formed trimeric coiled coil, and repositioning of the C-terminal membrane anchor near the fusion peptide at the same end of a rod-shaped molecule. Comparison of this new HA conformation, which has been formed for membrane fusion, with the structures determined for other virus fusion glycoproteins suggests that these molecules are all in the fusion-activated conformation and that the juxtaposition of the membrane anchor and fusion peptide, a recurring feature, is involved in the fusion mechanism. Extension of these comparisons to the soluble N-ethyl-maleimide-sensitive factor attachment protein receptor (SNARE) protein complex of vesicle fusion allows a similar conclusion.
02 Jun 1988-Nature
TL;DR: The three-dimensional structures of influenza virus haemagglutinins complexed with cell receptor analogues show sialic acids bound to a pocket of conserved amino acids surrounded by antibody-binding sites, suggesting that antibodies neutralize virus infectivity by preventing virus-to-cell binding.
Abstract: The three-dimensional structures of influenza virus haemagglutinins complexed with cell receptor analogues show sialic acids bound to a pocket of conserved amino acids surrounded by antibody-binding sites. Sialic acid fills the conserved pocket, demonstrating that it is the influenza virus receptor. The proximity of the antibody-binding sites suggests that antibodies neutralize virus infectivity by preventing virus-to-cell binding. The structures suggest approaches to the design of anti-viral drugs that could block attachment of viruses to cells.
01 Jan 1987-Annual Review of Biochemistry
Abstract: A number of glycoproteins have oligosaccharides linked to protein in a GlcNAc----asparagine bond. These oligosaccharides may be either of the complex, the high-mannose or the hybrid structure. Each type of oligosaccharides is initially biosynthesized via lipid-linked oligosaccharides to form a Glc3Man9GlcNAc2-pyrophosphoryl-dolichol and transfer of this oligosaccharide to protein. The oligosaccharide portion is then processed, first of all by removal of all three glucose residues to give a Man9GlcNAc2-protein. This structure may be the immediate precursor to the high-mannose structure or it may be further processed by the removal of a number of mannose residues. Initially four alpha 1,2-linked mannoses are removed to give a Man5 - GlcNAc2 -protein which is then lengthened by the addition of a GlcNAc residue. This new structure, the GlcNAc- Man5 - GlcNAc2 -protein, is the substrate for mannosidase II which removes the alpha 1,3- and alpha 1,6-linked mannoses . Then the other sugars, GlcNAc, galactose, and sialic acid, are added sequentially to give the complex types of glycoproteins. A number of inhibitors have been identified that interfere with glycoprotein biosynthesis, processing, or transport. Some of these inhibitors have been valuable tools to study the reaction pathways while others have been extremely useful for examining the role of carbohydrate in glycoprotein function. For example, tunicamycin and its analogs prevent protein glycosylation by inhibiting the first step in the lipid-linked pathway, i.e., the formation of Glc NAc-pyrophosphoryl-dolichol. These antibiotics have been widely used in a number of functional studies. Another antibiotic that inhibits the lipid-linked saccharide pathway is amphomycin, which blocks the formation of dolichyl-phosphoryl-mannose. In vitro, this antibiotic gives rise to a Man5GlcNAc2 -pyrophosphoryl-dolichol from GDP-[14C]mannose, indicating that the first five mannose residues come directly from GDP-mannose rather than from dolichyl-phosphoryl-mannose. Other antibodies that have been shown to act at the lipid-level are diumycin , tsushimycin , tridecaptin, and flavomycin. In addition to these types of compounds, a number of sugar analogs such as 2-deoxyglucose, fluoroglucose , glucosamine, etc. have been utilized in some interesting experiments. Several compounds have been shown to inhibit glycoprotein processing. One of these, the alkaloid swainsonine , inhibits mannosidase II that removes alpha-1,3 and alpha-1,6 mannose residues from the GlcNAc- Man5GlcNAc2 -peptide. Thus, in cultured cells or in enveloped viruses, swainsonine causes the formation of a hybrid structure.(ABSTRACT TRUNCATED AT 400 WORDS)