Oligosaccharides determinants

The final chapter, by Hounsell (London), also relates to an important aspect of glycoprotein structure, namely the structures and shapes, as determined by physicochemical methods, of oligosaccharide determinants of glycoproteins that are antigens and targets for binding of adhesion molecules. 

Fig. 4.5.2 Actual strategies for CDG diagnosis. Initial investigations on CDG patients are routinely carried out by isoelectric focusing (IEF) of serum transferrin. With a CDG type I pattern, subsequent analysis should imply determination of phosphomannomutase (PMM) and phos-phomannose isomerase (PMI) activities. Further studies, like analysis of the lipid-linked- and protein-bound-oligosaccharides, determination of enzyme or sugar transporter activities and molecular biology studies often have to be performed in more specialised laboratories. HPLC High-performance liquid chromatography, TLC thin-layer chromatography...

In many instances, the linkage oligosaccharide is associated with a peptide moiety, and thus the amino acid sequence must be established and, in addition, the structural parameters of the CPL oligosaccharide determined. The latter comprise (i) primary structure, (i i) type and location of noncarbohydrate substituents, and (i i i) the linkage to the peptide backbone. For gaining insight into structure-function relations, it is important for the three-dimensional structure to be determined. 

Selection procedure. This is basically done by exposing the cell population to an antibody specific for an exposed cell membrane component (e.g. a specific protein, or an oligosaccharide determinant), and then adding complement to lyse all the cells that have bound enough antibody to trigger a cytotoxic effect. A selection procedure carried out on cells in suspension is described next. The same selection can also be applied to cell monolayers. 

The antigenic variation of blood group substances is due to specific glycosyltransferases (the primary gene products) responsible for synthesis of the oligosaccharide determinants (the secondary gene products). 

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