PRIMARY STRUCTURE OF THE HETEROSACCHARIDE OF THE SURFACE GLYCOPROTEINOF METHANOTHERMUS-FERVIDUS

The outer surface of the cells of the hyperthermophile Methanothermus fervidus is covered by crystalline glycoprotein subunits (S-layer). Fr om the purified S-layer glycoprotein, a heterosaccharide was isolated. The heterosaccharide consists of D-3-O-methylmannose, D-mannose, and D-N-acetylgalactosamine in a molar ratio of 2:3:1 corresponding to a r elative molecular mass of 1061.83 Da. 3-O-methylmannose could be partl y replaced by 3-O-methylglucose. The primary structure of the glycan w as revealed by methylation analysis, by plasma desorption mass spectro metry, and by high field NMR spectroscopy. The purified heterosacchari de is linked via N-acetylgalactosamine to an asparagine residue of the peptide moiety. The following structure is proposed for the heterosac charide: alpha-D-3-O-MetManp-(1 --> 6)-alpha-D-3-O-MetManp-((1 --> 2)- alpha-D-Manp)3-(1 --> 4)-D-GalNAc.