All pyruvylated galactose in Schizosaccharomyces pombe N-glycans is present in the terminal disaccharide, 4,6-O-[(R)-(1-carboxyethylidine)]-Galβ1,3Galα1-

The large N-linked oligosaccharides released from Schizosaccharomyces pombe by endo-beta-N-acetylglucosaminidase H were examined to determine how the negatively charged pyruvylated galactoses present (Gemmill,T.R., and Trimble,R.B., 1996, J. Biol. Chem., 271, 25945-25949) were attached to the oligosaccharide chains. Binding of biotinylated human serum amyloid P and peanut agglutinin to native and depyruvylated S. pombe glycoproteins, respectively, indicated that the pyruvylated epitope was likely to be in the beta configuration. Examination by high-field H-1 NMR of whole glycans and a disaccharide fragment released from them on partial acid hydrolysis showed that the pyruvylated galactose species was in fact beta 1,3-linked to a second galactose, and this occurred an average of five to six times on nominal Ga(57)Man(64)GlcNAc N-glycans. The pyruvate-2,(4,6)Gal-beta 1,3Gal epitope is chemically similar to acetaldehyde-Gal beta 1,3Gal groups found on the glycoproteins from Paramyxovirus-infected bovine kidney cells (Prehm,P,, Scheid,A, and Choppin,P.W.,1979, J. Biol. Chem., 254, 9669-9677), The 1:1 stoichiometry between pyruvate and beta-linked galactose in these S. pombe glycans indicates that either pyruvate addition to terminal beta 1,3Gal is highly efficient or that pyruvylated Gal is transferred en bloc to alpha 1,2-linked Gal residues in the N-linked chains. In contradiction to many galactomannan-producing fungi, which add substantial amounts of Gal in the furanose form to their glycoproteins, all detectable Gal in the large S. pombe galactomannans is in the pyranose form, as found in higher eukaryotes, The current work shows that the S. pombe outer chain structure is a poly-alpha 1,6Man backbone 2-O-substituted with either Gal or the pyruvylated galactobiose and contains little aid-linked or 2-O-substituted Man. This is in contrast to the S. cerevisiae outer chain, which is poly-alpha 1,6Man substituted with alpha 1,2-linked Man sidechains (Ballou,C.E.,1990, Methods Enzymol, 185, 440-470).