Carbohydrate structures of the third component of rat complement. Presence of both high-mannose and complex type oligosaccharide chains

Biosensor based on lectin and lipid membranes for detection of serum glycoproteins in infected patients with dengue

In this work, we developed a biosystem based on Concanavalin A (ConA) and lipid membranes to recognize glycoproteins from the serum of patients contaminated with dengue serotypes 1, 2 and 3 (DENV1, DENV2 and DENV3). The modified gold electrode was characterized using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and atomic force microscopy. Morphological analyses of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), DPPC-ConA, DPPC-ConA-DENV1, DPPC-ConA-DENV2 and DPPC-ConA-DENV3 revealed the existence of a non-uniform covering and large globules. EIS and CV measurements have shown that redox probe reactions on the modified gold electrodes were partially blocked due to the adsorption of lipid-ConA system and reveal the interaction response of the immobilized ConA to the presence of glycoproteins of dengue serum. The biosystem exhibited a wide linear response to different concentrations of sera of dengue serotypes 1, 2 and 3. A higher impedimetric response to glycoproteins present in dengue serotype 3 was observed. Our results demonstrate the applicability of lectin and lipid membranes to the development of biosensors for dengue infections.

Structure of the major oligosaccharide of cobra venom factor

Cobra venom factor (CVF), the complement-activating glycoprotein in cobra venom, contains three or possibly four N-linked oligosaccharide chains per molecule and is devoid of O-linked saccharides. Analysis by lectin-affinity staining revealed the presence of complex-type oligosaccharides containing non-reducing terminal alpha-galactosyl residues and fucose residues linked to the proximal N-acetylglucosamine. Sialic acid residues could not be detected. For their structural analysis, the oligosaccharides were released by hydrazinolysis and fractionated on Bio-Gel P-4. Approximately 80% of the eluted oligosaccharides have a size equivalent of 17 +/- 2 glucose units. The major oligosaccharide representing about 45% of the total carbohydrate present in CVF was purified to homogeneity by MicroPak AX-5 HPLC and its structure was analyzed by sequential exoglycosidase digestion. The positions of the glycosidic linkages of the sugar residues were established by methylation analysis of CVF-derived glycopeptides. The data of these analyses indicated that the major oligosaccharide has a symmetrical fucosylated biantennary complex-type structure terminating with unusual alpha-galactosyl residues.

Carbohydrate analysis of glycoproteins. A review

Many of the products prepared by biotechnological approaches, including recombinant genetic engineering, cell tissue culture, and monoclonal technologies, are glycoproteins. As little as five years ago, glycosylation was believed to play no significant role in the function of glycoproteins. Recent large scale testing of glycoprotein-based pharmaceuticals has indicated that both the extent and type of glycosylation can play a central role in glycoprotein activity. Although methods for compositional and sequence analysis of proteins and nucleic acids are generally available, similar methods have yet to be developed for carbohydrate oligomers and polymers. This review focuses on new, developing methods for the analysis and sequencing of the carbohydrate portion of glycoproteins. Included are: (1) the release of oligosaccharides and hydrolysis of carbohydrate chains using enzymatic and chemical methods; (2) fractionation by LPLC, electrophoresis, HPLC, and lectin affinity chromatography; (3) detection through the preparation of derivatives or by new electrochemical methods; (4) analysis by spectroscopic methods, including MS and high-field NMR; and (5) their sequencing through the use of multiple, well-integrated techniques. The ultimate goal of the analytical approaches discussed is to firmly establish structure and, thus, permit the study of structure-function relationships and eventually to allow the intelligent application of carbohydrate remodeling techniques in the preparation of new glycoproteins.

The oligosaccharide chains of cobra venom factor are required for complement activation

To examine the function of the carbohydrate chains of cobra venom factor (CVF), the molecule was enzymatically deglycosylated under non-denaturing conditions with N-glycanase (peptide-N4-(N-acetyl-beta-glucosaminyl) asparagine amidase). The deglycosylation of CVF chains seems to proceed independently of each other, leading to partially deglycosylated intermediates. Complete deglycosylation of CVF was found to abolish the activity of CVF. The deglycosylated molecule is unable to activate the alternative pathway of complement. Deglycosylated CVF no longer consumes the serum complement activity, it does not induce C3 activation in serum, nor does it induce complement-mediated hemolysis. These results indicate that the carbohydrate moieties of CVF are essential for its role in complement activation.

Brefeldin A arrests the intracellular transport of a precursor of complement C3 before its conversion site in rat hepatocytes

The effects of brefeldin A on intracellular transport and posttranslational modification of complement C3 (C3) were studied in primary culture of rat hepatocytes. In the control culture C3 was synthesized as a precursor (pro-C3), which was processed to the mature form with alpha- and beta-subunits before its discharge into the medium. In the presence of brefeldin A the secretion of C3 was strongly blocked, resulting in accumulation of pro-C3. However, after a prolonged interval the mature form of C3 was finally secreted. The results indicate that brefeldin A impedes translocation of pro-C3 to the Golgi complex where pro-C3 is converted to the mature form, but not its proteolytic processing, in contrast to the effects of monensin and weakly basic amines.