Primary structure of the heterosaccharide of the surface glycoprotein of Methanothermus fervidus.

The outer surface of the cells of the hyperthermophile Methanothermus fervidus is covered by crystalline glycoprotein subunits (S-layer). From 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 relative molecular mass of 1061.83 Da. 3-O-methylmannose could be partly replaced by 3-O-methylglucose. The primary structure of the glycan was revealed by methylation analysis, by plasma desorption mass spectrometry, and by high field NMR spectroscopy. The purified heterosaccharide is linked via N-acetylgalactosamine to an asparagine residue of the peptide moiety. The following structure is proposed for the heterosaccharide: alpha-D-3-O-MetManp-(1-->6)-alpha-D-3-O-MetManp-((1-->2)-alp ha-D-Manp)3-(1-->4) - D-GalNAc.