Structure diantennary

FIG. 34.—Molecular Model of Diantennary Glycan of Human-serum Transferrin. [A, Y Conformation14 B, T Conformation. 4 Numbers correspond to the numbering used in Table II (see fundamental structure).]... 

Compound 6 can be isolated62 from the urine of patients with Sand-hoff s disease (GM2-gangIiosidosis variant O). The 500-MHz, H-n.m.r. spectrum of this reducing oligosaccharide is depicted in Fig. 6 its spectral parameters are compiled in Table IV. Compound 6 contains the 3,6-disubstituted Man-3, characteristic for diantennary structures. Each branch is terminated with a /3-(l— 2)-linked GlcNAc residue. 

Compound 7 is a so-called diantennary oligosaccharide it can be isolated from the urine of patients suffering from GMj-gangliosi-dosis,52,63-643 as well as from64,65 Morquio syndrome type B. The 500-MHz, H-n.m.r. spectrum of 7 is presented in Fig. 7, and the chemical shifts of the structural-reporter groups are summarized in Table IV. 

The chemical shifts of the structural-reporter groups of Gal-6 and GlcNAc-5 are in full accord with those observed for the corresponding protons in the diantennary oligosaccharide 7 (see Table IV). The chemical shift and the line width of the H-l doublet of GlcNAc-5 differ considerably from those observed for GlcNAc-5 in the spectrum of 17 (see Fig. 18a). The chemical shifts of the H-l and H-2 atoms of Man-4 reflect the incompleteness of the branching core (compare with 6, 7, 19, and 20 see Tables IV and VIII). 

For the spectral interpretation, 19 is considered as being structure 17 extended with Man-4, a-( 1—>6)-linked to Man-3. The attachment of Man-4 leads to chemical shifts for H-l of the a anomer of GlcNAc-2 and for the N-acetyl protons of 2 for both anomers of 19, which are identical to those for the diantennary compound 7 (at 300 K, the /3-anomeric, H-l signal of GlcNAc-2 is partially hidden under the HOD line). 

Compounds 25 and 26 are reducing oligosaccharides having incomplete, diantennary structures. They were isolated from new-born, human meconium76 in a mixture containing 25 and 26 in the ratio of 3 1. The 500-MHz, H-n.m.r. spectrum of the mixture is shown in Fig. 22, and the n.m.r. data for both compounds are compiled in Table IX. 

The location of NeuAc in a diantennary, monosialo structure may be directly inferred from the chemical-shift values of the H-l signals of Man-4 and -4. The chemical shifts of the N-acetyl signals of GlcNAc-5 and -5 also reflect whether or not a certain branch is terminated with a NeuAc residue in a-(2- 6) linkage to Gal. In principle, the chemical... 

The pattern of the signals of the H-l and H-2 resonances of Man residues 3,4, and 4 is, as a whole, typical of a diantennary, sialo structure wherein the chemical shifts of the H-l signals of Man-4 and -4 indicate that each branch is terminated with NeuAc in -(2—>6) linkage to Gal. 

For locating an a-(2— 3)-linked NeuAc in one of the branches of a diantennary, monosialo structure, the combination of three effects is... 

The spectrum of 39 (see Fig. 30) clearly illustrates that the sets of chemical shifts for the NeuAc H-3 signals are characteristic for the a-(2—>3) or a-(2— 6) type of linkage to the Gal residue of an N-acetyllac-tosamine moiety. These values of chemical shift are independent of elongation of the other branch in a diantennary structure by NeuAc in any type of linkage. 

Fig. I. Core structures of the carbohydrate units of nervous tissue glycoproteins. The structures are based on analytical data on rat brain glycoproteins and on assumptions of structural similarity with glycan cores from other sources. The main positions of variable or incomplete glycosylation are indicated by arrows. The approximate molar proportions of the glycans in rat brain and the mode of interaction with concanavalin A-Sepharose are indicated (the bisecting GicNAc residue affects the interaction of the diantennary glycans with concanavalin A) [9].

Gal(al-3)Gal group and 23% of the diantennary complex-type glycans contained the bisecting GlcNAc residue. These structures were not detected in the glycans of human plasma factor VIII. 

The structure of some of these oligosaccharides has been determined. A major N-glycan representing about 45% of the carbohydrate chains is a monosialylated monofucosylated diantennary glycan of the V-acetyllactosaminic type (Fig. 12A)[81]. A tetraantennary glycan of the V-acetyllactosaminic type has also been isolated and its structure determined by methylation analysis and 500MHz H-NMR (Fig. 12B)[82]. The major O-glycan of human vWf was shown to be a diantennary tetrasaccharide (Fig. 12C)[83]. 

Fig. 6. Primary structure of serotransferrin diantennary glycans from human (A,B) [211-213], cow (A,B) [119, 214], rabbit (A) [103], sheep (A) [119,215], marsupial (kangaroo, opossum, wallaby) (A) [119,216], Primary structure of human serotransferrin triantennary glycans (C,D) [119-217],...

Interestingly, the glycan primary structure of lactotransferrin extracted from human polymorphonuclear leukocytes is identical to that of the non-fucosylated diantennary... 

Fig. 14. Primary structure of diantennary glycans from cow lactotransferrin with an a-l,3-Gal residue in the terminal position [119,236] and with a GalNAc residue replacing a Gal residue.

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