NOVEL N-GLYCOSYLATION IN EUKARYOTES - LAMININ CONTAINS THE LINKAGE UNIT BETA-GLUCOSYLASPARAGINE

The linkage unit to protein of N-linked carbohydrate in eukaryotic gly coproteins consists of N-acetylglucosamine, coupled to the amido nitro gen of asparagine. Additional N-glycosyl linkage units have been unequ ivocally proven to exist only in the cell surface glycoproteins of var ious bacteria. Based on immunological analyses, isolation and chemical characterization, we report that one of these units, namely glucose l inked to asparagine, exists in the mammalian protein laminin, an extra cellular basement membrane component. This finding and the occurrence of identical disaccharide structures in archaebacterial cell surface g lycoproteins and mammalian basement membrane protein complexes points towards a conserved and distinct function of these extracellular struc tural elements. In addition, a method is described to uncover a masked epitope in fixed tissues by chemical O-deglycosylation. This has allo wed to morphologically localize the antigen beta-Glc-Asn by immunofluo rescence to the basement membranes of kidney glomeruli.