Negligible elongation of mucin glycans with Gal beta 1-3 units distinguishes the laminated layer of Echinococcus multilocularis from that of Echinococcus granulosus

The larval stages of the cestodes Echinococcus multilocularis and Echinococcus granulosus cause the important zoonoses known as larval echinococcoses. These larvae are protected by a unique, massive, mucin-based structure known as the laminated layer. The mucin glycans of the E. granulosus laminated layer are core 1- or core 2-based O-glycans in which the core Galp beta 1-3 residue can initiate a chain comprising one to three additional Galp beta 1-3 residues, a motif not known in mammalian carbohydrates. This chain can be capped with a Galp alpha 1-4 residue, and can be ramified with GlcNAcp beta 1-6 residues. These, as well as the GlcNAcp beta 1-6 residue in core 2, can be decorated with the Galp alpha 1-4Galp beta 1-4 disaccharide. Here we extend our analysis to the laminated layer of E. multilocularis, showing that the non-decorated cores, together with Galp beta 1-3(Galp alpha 1-4Galp beta 1-4GlcNAcp beta 1-6)GalNAc , comprise over 96% of the glycans in molar terms. This simple laminated layer glycome is exhibited by E. multilocularis grown either in vitro or in vivo. Interestingly, all the differences with the complex laminated layer glycome found in E. granulosus may be explained in terms of strongly reduced activity in E. multilocularis of a putative glycosyltransferase catalysing the elongation with Galp beta 1-3. Comparative inter-species analysis of available genomic and transcriptomic data suggested a candidate for this enzyme, amongst more than 20 putative (non-core 1) Gal/GlcNAc beta 1-3 transferases present in each species as a result of a taeniid-specific gene expansion. The candidate gene was experimentally verified to be transcribed at much higher levels in the larva of E. granulosus than that of E. multilocularis.