Core tetrasaccharide liberated by endo-beta-D-N-acetylglucosaminidase D from lactosamine-type oligosaccharides of Semliki Forest virus membrane proteins.

[3H]Mannose- and [3H]glucosamine-labeled lactosamine-type glycopeptides of Semliki Forest virus membrane proteins were stripped of their fucose, sialic acid, galactose and distal N-acetylglucosamine residues and subsequently digested with endo-beta-D-N-acetylglucosaminidase D from Diplococcus pneumoniae. Two products were obtained, a neutral tetrasaccharide and a residual glycopeptide fraction. The tetrasaccharide appeared to consist of two alpha-mannose residues, one beta-mannose residue and one N-acetylglucosamine residue located at the reducing terminus of the molecule. Results of Smith degradation, beta-elimination and acetolysis were compatible with four structures; (1) Man alpha-1-3[Man alpha 1-6]Man beta 1-4GlcNAc; (2) Man alpha 1-3Man beta 1-4[Man alpha 1-6] GlcNAc; (3) Man alpha 1-3Man alpha 1-4[Man beta 1-6]GlcNAc, or (4) Man alpha 1-6Man alpha 1-3Man beta-1-4GlcNAc. The reactivity of the viral glycopeptides with endo-beta-D-N-acetylglucosaminidase D and the chromatographic properties of the liberated core tetrasaccharide suggest that its most likely structure was Man alpha 1-3[Man alpha-1-6]Man beta 1-4GlcNAc. The core tetrasaccharide of glycans of membrane protein E3, one of the viral membrane proteins obtained from infected cell, was similar to that of the virion glycans.