Identification of a novel oligosaccharide backbone structure with a galactose residue monosubstituted at C-6 in human foetal gastrointestinal mucins

Glycoprotein oligosaccharides as recognition structures

A series of observations--the pronounced changes in the expression and distribution of oligosaccharide antigens during embryonic development, cell differentiation and oncogenesis, the prominence of these changing structures (oncodevelopmental antigens) on the receptor for epidermal growth factor, and the stimulation of receptor autophosphorylation following their perturbation with antibodies--has suggested that the oligosaccharides of growth factor receptors and complementary lectins may be intimately involved in molecular recognition events in growth and differentiation processes. For elucidating oligosaccharide recognition by diverse cellular and secreted proteins and microbial adhesins, a new technique has been developed which involves the overlay of immobilized oligosaccharide probes (neoglycolipids) derived from glycoproteins and other sources. New insights have been gained into carbohydrate recognition by several mammalian lectins, and a novel receptor system has been discovered in Escherichia coli isolated from patients with urinary tract infections. This new technique seems ideal for elucidating oligosaccharide recognition in diverse biological settings, and for 'quality control' of the sugar chains of recombinant glycoproteins engineered for the purpose of administration to man.

1H NMR analysis of novel sialylated and fucosylated lactose-based oligosaccharides having linear GlcNAc(beta 1-6) Gal and Neu5Ac(alpha 2-6) GlcNAc sequences

Three novel oligosaccharides of human infant faeces have been fully characterised by methylation analysis and 500/600 MHz 1H NMR spectroscopy including DQF-COSY, TQF-COSY, TOCSY and ROESY experiments. The oligosaccharides were shown to be lactose-based structures two of which were substituted at C-6 of Gal with either the Le(x) trisaccharide, Gal(beta 1-4)[Fuc(alpha 1-3)]GlcNAc(beta 1-, or Neu5Ac(alpha 2-6)Gal(beta 1-4)GlcNAc(beta 1-. They differ from other free oligosaccharides previously isolated from the human by having the (1-->6) linkage to Gal in the absence of a (1-->3) branch. The third oligosaccharide has Neu5Ac(alpha 2-6) linked to GlcNAc of the trisaccharide GlcNAc(beta 1-3)Gal(beta 1-4)Glc. This is a linear fragment of the disialylated tetrasaccharide sequence Neu5Ac(alpha 2-3)Gal(beta 1-3)[Neu5Ac(alpha 2-6)]GlcNAc(beta 1-found in the milk oligosaccharide disialyl LNT (the GlcNAc residue of the tetrasaccharide linked to lactose) and also of N-linked chains (GlcNAc linked to Man).

A novel beta-N-acetylglucosaminidase activity in hog gastric mucosal microsomes: preferential hydrolysis of terminal GlcNAc beta 1-3 linkages in GlcNAc beta 1-3(GlcNAc beta 1-6)Gal beta 1-4GlcNAc, but GlcNAc beta 1-6 linkages in GlcNAc beta 1-3(GlcNAc beta 1-6)Gal

Hog gastric mucosal microsomes contain beta-N-acetylglucosaminidase activity which cleaves GlcNAc beta 1-3(GlcNAc beta 1-6)Gal beta 1-4GlcNAc at the terminal GlcNAc beta 1-3Gal linkage faster than at the GlcNAc beta 1-6Gal bond, producing mainly GlcNAc beta 1-6Gal beta 1-4GlcNAc. In a marked contrast, GlcNAc beta 1-3(GlcNAc beta 1-6)Gal is cleaved primarily at the GlcNAc beta 1-6Gal bond, while partial hydrolysis of GlcNAc beta 1-3(GlcNAc beta 1-6)Gal beta 1-4Glc reveals similar rates of cleavage for the (1-3) and (1-6) linkages. Our data support the notion that the terminal beta 1,6-linked GlcNAc unit of GlcNAc beta 1-3(GlcNAc beta 1-6)Gal beta 1-4GlcNAc may interact with the reducing end GlcNAc unit intramolecularly in water solution.

Conformational studies of the backbone (poly-N-acetyllactosamine) and the core region sequences of O-linked carbohydrate chains

The AMBER forcefield with added carbohydrate specific parameters for potential types, charges and anomericity has been used to explore the conformational space sampled by oligosaccharides of repeating (Gal beta 1-4GlcNAc beta 1-3)n sequence and those having alpha chain terminating substituents on a Gal beta 1-3GalNAc alpha, O-glycosylated core. The 17 lowest energy forms of the 16-mer N-acetyllactosaminic sequence included fully extended units and spring-like coils with dielectric constant 80 to simulate a water environment. More restricted stereochemistry was exhibited by the glycosylation adjacent to the core as has been previously predicted by n.m.r. studies.

Characterisation of minor tetra- to hepta-saccharides O-linked to human meconium glycoproteins by t.l.c.-m.s. microsequencing of neoglycolipid derivatives in conjunction with conventional m.s. and 1H-n.m.r. spectroscopy

As part of the establishment of a data base for core and backbone sequences of O-linked oligosaccharides of human meconium glycoproteins, the minor tetra- to hepta-saccharides released from mild-acid treated blood group [corrected] H-active glycoproteins have been studied. These oligosaccharides are heterogeneous and difficult to isolate, and a t.l.c.-m.s. microsequencing procedure has been applied to the neoglycolipid derivatives, in conjunction with 1H-n.m.r. spectroscopy, methylation analysis, and mass spectrometry (m.s.) of native and methylated oligosaccharides. Among an array of oligosaccharides characterised are those having the branched beta-GlcNAc-(1----6)[beta-Gal- (1----3)]-GalNAcol core, and others with the following linear sequences not characterised previously from this source: beta-Gal-(1----3)-beta-GlcNAc-(1----3)-beta-Gal-(1----3)-GalNAcol, beta-Gal-(1----4)-beta-GlcNAc-(1----3)-beta-Gal-(1----3)-GalNAcol, alpha-GalNAc- (1----3)-beta-Gal-(1----3/4)-beta-GlcNAc-(1----3)-GalNAcol, beta-GlcNAc- (1----3)-beta-Gal-(1----3/4)-beta-GlcNAc-(1----3)- GalNAcol, beta-Gal-(1----3/4)-beta-GlcNAc-(1----3)-beta-Gal-(1----3/4)-beta- GlcNAc-(1----3)-beta-Gal-(1----3)-GalNAcol, and beta-GlcNAc-(1----3)-beta-Gal-(1----3/4)-beta-GlcNAc-(1----3)-beta-Gal- (1----3/4)-beta-GlcNAc-(1----3)-GalNAcol.

Single mid-chain GlcNAc beta 1-6Gal beta 1-4R sequences of linear oligosaccharides are resistant to endo-beta-galactosidase of Bacteroides fragilis

Endo-beta-galactosidase (EC 3.2.1.103) of Bacteroides fragilis, at 250 mU ml-1, did not cleave the internal galactosidic linkage of the linear radiolabelled trisaccharide GlcNAc beta 1-6Gal beta 1-4GlcNAc, or those of tetrasaccharides Gal beta 1-4GlcNAc beta 1-6Gal beta 1-4GlcNAc and Gal beta 1-4GlcNAc beta 1-6Gal beta 1-4Glc. The isomeric glycans which contained the GlcNAc beta 1-3Gal beta 1-4GlcNAc/Glc sequence were readily cleaved.

Computer-assisted interpretation of 1H-n.m.r. spectra in the analysis of the structure of oligosaccharides

A computer program that can be implemented on IBM compatible microcomputers has been used to interpret the 1H-n.m.r. spectra of a series of mucin-derived alditols. The program compares the chemical shifts of resonances in the spectra of unknown oligosaccharides with those in a standard library constructed from data in the literature. The program then compiles the identified sequences into possible structures, which, together with a second component of the program from which the individual assignments of chemical shifts can be made, facilitates ready access to the literature data for final confirmation of the structures.

Characterisation by mass spectrometry and 500-MHz proton nuclear magnetic resonance spectroscopy of penta- and hexasaccharide chains of human foetal gastrointestinal mucins (meconium glycoproteins)

Structural studies using liquid secondary ion mass spectrometry, gas liquid chromatography/mass spectrometry and 500-MHz 1H NMR are described of the major penta- and hexasaccharides of a fraction of human foetal gastrointestinal mucins. Glycoproteins from a blood group H active meconium pool were studied after depletion of Ii antigenic activities by immunoaffinity chromatography and treatment with mild acid hydrolysis to reduce the chain heterogeneity. Oligosaccharides were released by mild alkali/borohydride degradation and purified by Bio-Gel P4 chromatography and HPLC. Eleven penta- and hexasaccharides have been fully characterised as a result of this study and one previous report [Hounsell et al. (1988) Biochem. J. 256, 397-401] and information obtained on additional oligosaccharides present in small amounts. These oligosaccharides show the following features: (table; see text) Sequences in these oligosaccharides not commonly found in mucins so far studied are chain-terminating GlcNAc alpha 1-4Gal, repeating-type-I (Gal beta 1-3GlcNAc) backbones, the backbone branch GlcNAc beta 1-6(GlcNAc beta 1-3)Gal and the backbone sequence GlcNAc beta 1-6Gal beta 1- in the absence of a substituent at C3 of galactose.