Glycoepitopes of N-glycans in Echinodermata

Great advances have been made in recent years as regards genomic comparisons between organisms due to the large number of genome sequencing projects. In part these studies have altered our view of the phylogeny of organisms. However, the comparison of protein-linked carbohydrates, e.g., N-linked glycans, between organisms continues to lag behind due to the complicated nature of glycan analyses. On the other hand, glycans in their various types have key roles in development and morphogenesis as they cover the surfaces of all cells and so are involved in a wide range of cell-cell interactions. In this project, it is proposed to focus on the N-linked glycans of the echinodermata, a group of marine organisms including starfish and sea urchins, which are ‘advanced’ invertebrates, but are still not members of the chordata, a group including the vertebrates. Despite the evolutionary and phylogenetic importance of the transition to the vertebrate state, a process undoubtedly accompanied by new cell-cell interactions, there are few data regarding the glycans of the organisms which are in the ‘grey zone’ between typical invertebrates (e.g., worms and insects) and vertebrates (including humans). Therefore, the N-glycans of selected echinodermata will be released, purified and analysed, in particular by mass spectrometry. Based on genomic data on the sea urchin (Strongylocentrotus purpuratus) and on preliminary lectin-binding data, it can be hypothesised that the glycans of the sea urchin and other echinodermata contain fucose and sialic acid, the latter being a component normally associated with vertebrates. The fine detail of the N-glycans of these organisms will be assessed by MS/MS and HPLC analyses in conjunction with exoglycosidase and chemical treatments. Correlations between the loss or gain of carbohydrate epitopes will be made with genomic and enzymatic data. The result of these glycomic analyses will be a deeper understanding of a group of key post-translational modifications on proteins of a phylum at an important evolutionary nexus in the transition to the emergence of vertebrates.