Evaluation of recombinant glycoproteins

Glycoaffinity chromatography and biological recognition

The potential of bioaffinity chromatography as a tool for study of biological recognition mechanisms is gaining increasing recognition. Biochromatographic methods allow the separation of proteins according to both the structure of their polypeptidic chain and their post-translational modifications. Among the various post-translational modifications which proteins undergo, glycosylation has conducted to the development of original methods (glycotechnologies). This review discusses the applications of glycotechnologies in bioaffinity chromatography, and particularly the use of biochromatography to elucidate mechanisms involved in glycobiology.

The analysis of fluorophore-labeled carbohydrates by polyacrylamide gel electrophoresis

The glycans of glycoconjugates mediate numerous important biological processes. Their separation and structural determination present considerable difficulties because of the small quantities that are available from biological sources and the inherent difficulty of analyzing the wide variety of complex structures that exist. A method for the analysis of reducing saccharides by PAGE that uses specific fluorophore labeling and is simple, rapid, sensitive, and readily available to biological researchers, has been developed. This method is known acronimically either as PAGEFS (PAGE of Fluorophore-labeled Saccharides) or in one commercial format as FACE (Fluorophore-Assisted Carbohydrate Electrophoresis). In the PAGEFS method, saccharides having an aldehydic reducing end group are labeled quantitatively with a fluorophore and then separated with high resolution by PAGE. Two fluorophores, 8-aminonaphthalene-1,3,6-trisulfonic acid (ANTS) and 2-aminoacridone (AMAC), have been used to enable the separation of a variety of saccharide positional isomers, anomers, and epimers. Subpicomolar quantities of individual saccharides can be detected using a sensitive imaging system. Mixtures of oligosaccharides obtained by enzymatic cleavage from glycoproteins can be labeled and electrophoresed to yield an oligosaccharide profile of each protein. AMAC can be used to distinguish unequivocally between acidic and neutral oligosaccharides. Methods of obtaining saccharide sequence information from purified oligosaccharides have been developed using enzymatic degradation. Other applications and the potential of the system are described.

Endo beta-N-acetylglucosaminidase F cleavage specificity with peptide free oligosaccharides

Endo beta-N-acetylglucosaminidase activities were determined based on conversion of oligosaccharides containing two N-acetylglucosamines to the oligosaccharides with a single N-acetylglucosamine at the reducing terminal and following their separation on a carbohydrate analyzer. The oligosaccharides eluted from the high performance anion exchange column in the order of fucosyl-N,N'-diacetylchitobiose, N,N'-diacetylchitobiose and N-acetylglucosamine containing reducing terminals. Using this assay, differences in cleavage specificity of the endo beta-N-acetylglucosaminidase F (Endo F) activity on various free oligosaccharides obtained from the standard glycoproteins was determined. The commercial Endo F-peptide N-glycosidase/glycanyl amidase (PNGase) mixture readily cleaved high mannose and complex oligosaccharides (neutral and sialyated) with common core alpha 1-6 linked fucose found in porcine thyroglobulin including the trimannosyl-chitobiose core structure. However, the same Endo F mixture did not cleave the non-fucosylated complex oligosaccharides found in human transferrin and also the common core structure. Glycopeptide counterparts with and without fucose were good substrates for the endoglycosidases. These results show that the specificity of these enzymes is such that they can recognize the conformational differences between free oligosaccharides and glycopeptides with and without the common core alpha 1-6 linked fucose. In contrast, highly purified Endo F cleaved only the high mannose type oligosaccharides and was unable to cleave ovalbumin hybrid type oligosaccharides.(ABSTRACT TRUNCATED AT 250 WORDS)