Recent data on the structure of the carbohydrate moiety of glycoproteins. Metabolic and biological implications

The author reviews the information acquired in the last four years on the structure of isoglycans (branched glycans) N-glycosidically linked to asparagine.Developments of the structural methodology of conjugated carbohydrates are analysed with reference to the following procedures: sugar determination, chemical (partial acid hydrolysis, acetolysis, hydrazinolysis-nitrous deamination), and enzymatic (exo-and endoglycosidases) cleavage of polysaccharide chains, and methylation.Several structures of glycans are described.lt appears that all possess the common pentas..:ccharidic core of the following mannotriosido-di-N-acetylchitobiose Mancx-(1-+ 3) [Mancx-( l-+6)] Manß-( l-+4 )GlcNAcß-( l-+4)GlcNAcß-(l-+ )Asn on which are conjugated either neuraminyl (or fucosyl)-N-acetyllactosamine or oligomannoside residues.It is proposed to term these glycan structures, respectively, N-acetyllactosaminic type and oligomannosidic type.The author demonstrates that these structures are in a good agreement with recent data concerning, on the one hand, the biosynthesis and pathological catabolism of glycoproteins and, on the other hand, the biological role of carbohydrate moieties considered as cell recognition signals.