Structure elucidation and immunological activity of a novel glycopeptide from mannatide

•A novel water-eluted glycopeptide was obtained from mannatide.•Structure of polysaccharide moiety of the glycopeptide was determined.•The immunological activity of glycopeptides was compared. A water-soluble glycopeptide, designated as MTW, was isolated and purified from crude mannatide by DEAE-Sepharose. MTW showed one symmetrical peak on HPGPC with an average molecular weight of 2.95×104Da. MTW contained 16 kinds of amino acids and the total amino acid content was 0.95%. The structure of polysaccharide moiety of MTW was elucidated based on monosaccharide composition, methylation analysis, partial acid hydrolysis, IR and 1D/2D NMR spectroscopy. The results showed that MTW was a homogeneous glycopeptide including mannose and glucose with a molar ratio of 2:1. The polysaccharide moiety of MTW had a backbone of (1→6)-α-d-Man p residues, which highly branched at O-2 position of (1→2,6)-α-d-Man p residues. The side chains were mainly composed of (1→)-α-d-Man p, (1→2)-α-d-Man p, (1→4)-α-d-Glc p, (1→4,6)-α-d-Glc p residues. The backbone of the polysaccharide moiety of MTW was the same as MT2-A (Li et al. [1]), which was the main component of mannatide, but the side chains of MTW were somewhat different from that of MT2-A. Complement-fixation test indicated that MTW had the same beneficial effect on immunological activity as MT2-A.