Neutral N-glycans in adult rat brain tissue

Complete characterisation reveals fucosylated hybrid and complex structures

Authors


  • Correspondence to D. R. Wing, Glycobiology Institute, Department of Biochemistry, University of Oxford, South Parks Road, Oxford, England OX1 3QU

  • Fax: +44 1865 275216.

  • E-mail:drw@glycob.ox.ac.uk

  • URL:http://www.bioch.ox.ac.uk

  • Abbreviations. The nomenclature for describing oligosaccharide structures is as follows : A(1,2,3,4) indicates the number of antennae linked to the trimannosyl core; G(0−4) indicates the number of terminal galactose residues in the structure; F, core fucose; B, bisecting N-acetylglucosamine. For example, A2G0FB indicates a diantennary oligosaccharide with no terminal Gal residues, a core Fuc and a bisecting GlcNAc. MALDI-MS, matrix-assisted laser-desorption ionisation mass spectrometry; MAG, myelin-associated glycoprotein; N-CAM, neural cell adhesion molecule; TN-R, tenascin-R; NPGU, normal-phase glucose unit; NP-HPLC, normal-phase HPLC; RP-HPLC, reverse-phase HPLC; NeuAc, N-acetylneuraminic acid; 2D, two-dimensional.

  • Enzymes.β-Galactosidase ( EC3.2.1.23); β-hexosaminidase ( EC3.2.1.52); α-mannosidase ( EC3.2.1.24); 1,3/4-α-fucosidase ( EC3.2.1.111); 1,2/6-α-fucosidase ( EC3.2.1.51).

Abstract

Oligosaccharides expressed on cell surface and extracellular matrix glycoconjugates are potentially of crucial importance in determining many cell interactions. The complexity of cellular organisation of the brain and suggested involvement of N-glycosylation in neural development, make this an ideal system to study the potential role of glycosylation in tissue development, maintenance and function. Neural tissues are known to contain some highly unusual glycan structures but the structures expressed in neural tissue have not as yet been studied systematically. As a first initiative to assess the type of N-glycosylation occurring in neural tissue, we have characterised all of the major neutral N-linked oligosaccharides expressed in adult rat using a combination of matrix-assisted laser-desorption ionisation mass spectrometry, exoglycosidase sequencing combined with normal-phase HPLC, and two-dimensional HPLC mapping. Oligomannosidic glycans, Man(9−5)GlcNAc2, constituted approximately 15 % of the total brain N-glycan pool. The other neutral N-glycan components consisted of a series of diantennary structures (6.5 %), (2,6)-branched triantennary glycans (1 %) and hybrid structures (3 %). Both the complex and hybrid N-glycans were characterised by the presence of outer-arm α(1,3)-fucosylation (forming the Lewisx determinant), α(1,6)-core fucosylation and a bisecting GlcNAc residue. Some of these are unusual or novel structures not having been reported elsewhere. A large proportion of the diantennary N-glycans either lacked Gal residues entirely or were unsubstituted on one Man residue of the trimannosyl core, notably the Man α(1,3)-arm. This isomeric form is indicative of the action of a novel β-hexosaminidase activity and suggests a modification in the classical biosynthetic pathway for N-linked oligosaccharides. Furthermore, expression of large amounts of oligomannosidic glycans is not usually associated with tissue glycoproteins and suggests a possible involvement of these structures in neural cell interactions.

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