Sulphated and sialylated N-glycans in the echinoderm Holothuria atra reflect its marine habitat and phylogeny

Among the earliest deuterostomes, the echinoderms are an evolutionary important group of ancient marine animals. Within this phylum, the holothuroids (sea cucumbers) are known to produce a wide range of glycoconjugate biopolymers with apparent benefits to health; therefore, they are of economic and culinary interest throughout the world. Other than their highly modified glycosaminoglycans (e.g. fucosylated chondroitin sulfate and fucoidan), nothing is known about their protein-linked glycosylation. Here we used multistep N-glycan fractionation to efficiently separate anionic and neutral N-glycans before analyzing the N-glycans of the black sea cucumber (Holothuria atra) by MS in combination with enzymatic and chemical treatments. These analyses showed the presence of various fucosylated, phosphorylated, sialylated, and multiply sulfated moieties as modifications of oligomannosidic, hybrid, and complex-type N-glycans. The high degree of sulfation and fucosylation parallels the modifications observed previously on holothuroid glycosaminoglycans. Compatible with its phylogenetic position, H. atra not only expresses vertebrate motifs such as sulfo- and sialyl-Lewis A epitopes but displays a high degree of anionic substitution of its glycans, as observed in other marine invertebrates. Thus, as for other echinoderms, the phylum- and order-specific aspects of this species' N-glycosylation reveal both invertebrate- and vertebrate-like features.