Further structural characterization of the Echinococcus granulosus laminated layer carbohydrates: The blood-antigen P1-motif gives rise to branches at different points of the O-glycan chains

Abstract

The glycobiology of the cestodes, a class of parasitic flatworms, is still largely unexplored. An important cestode species is Echinococcus granulosus, the tissue-dwelling larval stage of which causes hydatid disease. The E. granulosus larva is protected from the host by a massive mucin-based extracellular matrix termed laminated layer (LL). We previously reported ( Díaz et al. 2009. Biochemistry 48:11678-11691) the molecular structure of the most abundant LL O-glycans, comprising up to six monosaccharide residues. These are based on Cores 1 and 2, in cases elongated by a chain of Galpβ1-3 residues, which can be capped by Galpα1-4. In addition, the Core 2 GlcNAcp residue can be decorated with the Galpα1-4Galpβ1-4 disaccharide. Larger glycans also detected contained additional HexNAc residues that could not be explained by the structural repertoire described above. In this work, we elucidate, by mass spectrometry (MS) and nuclear magnetic resonance (NMR), six additional glycans from the E. granulosus LL between six and eight residues in size. Their structures are related to those already described but in cases bear GlcNAcpβ1-6 or Galpα1-4Galpβ1-4GlcNAcpβ1-6 as ramifications on the core Galpβ1-3 residue. We also obtained evidence that noncore Galpβ1-3 residues can be similarly ramified. Thus, the new motif together with the previous information may explain all the glycan compositions detected in the LL by MS. In addition, we show that the anti-Echinococcus monoclonal antibody E492 (Parasite Immunol 21:141, 1999) recognizes Galpα1-4Galpβ1-4GlcNAcp (the blood P(1)-antigen motif). This explains the antibody's reactivity with a range of Echinococcus tissues, as the P(1)-motif is also carried on non-LL N-glycans and glycolipids from this genus.

Biology and Systematics of Echinococcus

“…The laminated layer comprises a specialised extracellular matrix unique to Echinococcus (Fig. 7), whose synthesis is a major metabolic activity of the much thinner germinal layer (Diaz et al, 2011a;Lin et al, 2012;Parkinson et al, 2012). It is a carbohydrateeprotein complex of highly glycosylated mucin glycoproteins (Kilejian and Schwabe, 1971).…”

“…p0235 Smyth (1969) commented on the significance of the presence of a human blood group P-like substance in the laminated layer of Echinococcus and its significance as a model system in better understanding the immunological basis of the hosteparasite relationship. This P1 blood-antigen motif has since attracted much attention and has been further characterized as a proteinecarbohydrate, trisaccharide/mucin complex containing galactosamine, yet no biological function has been described to date (Lin et al, 2012). Recently, however, Nicolao et al (2014) described the expression of an ATP-dependent transporter, P-glycoprotein in E. granulosus (EgPgp).…”

Unconventional Maturation of Dendritic Cells Induced by Particles from the Laminated Layer of Larval Echinococcus granulosus

“…Certain of these N-terminal extensions bear unpaired cysteine residues, coincident with evidence that disulfide bonds contribute to the LL structure (7). The LL mucin glycans are now largely defined (13, 14). …”

Parasite molecules and host responses in cystic echinococcosis

“…It makes sense that most of these antibodies are specifically bound to the mucin glycans, that is that the LL is antigenic. When the fragmentary information available is put together, including data for E. multilocularis , the suggestion reached is that a major antigenic carbohydrate motif in E. granulosus infection may be the Galα1‐4Galβ1‐3Gal trisaccharide, which terminates many LL O ‐glycans . Whether in the infection context the LL suffices to generate anticarbohydrate antibody responses or there is a role for priming by oncosphere (and in secondary infection, PSC) glycans is not known.…”