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

Abstract

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.