Glycome project: concept, strategy and preliminary application to Caenorhabditis elegans

Glycans play a central role as potential mediators between complex cell societies, because all living organisms consist of cells covered with diverse carbohydrate chains reflecting various cell types and states. However, we have no idea how diverse these carbohydrate chains actually are. The main purpose of this article is to persuade life scientists to realize the fundamental importance of taking some action by becoming involved in "glycomics". "Glycome" is a term meaning the whole set of glycans produced by individual organisms, as the third bioinformative macromolecules to be elucidated next to the genome and proteome. Here a basic strategy is presented. The essence of the project includes the following: (a) glycopeptides, but not glycans released from their core proteins, are targeted for linkage to genome databases; (b) Caenorhabditis elegans is used as the first model organism for this project, since its genome project has already been completed; (c) four essential attributes are adopted to characterize each glycopeptide: (i) cosmid identification number (ID), (ii) molecular weight (M(r)), (iii) retention (Rs) of pyridylaminated (PA) oligosaccharides in 2-D mapping, and (iv) dissociation constants (Kd's) of PA-oligosaccharides for a set of lectins. Thus, the obtained ID, M(r), R and Kd's construct the glycome database, which will be open as the previous genome and proteome databases. For the project to proceed the "glyco-catch" method is proposed, where a group of target glycopeptides are captured by means of lectin-affinity chromatography after protease digestion. Already glycopeptides from asialofetuin and ovalbumin were successfully captured by galectin-agarose and Con A-agarose, respectively. Further, to examine the practical validity of the method, we extracted membrane proteins from C. elegans with 1% Triton X-100, and isolated specific glycopeptides by use of the same galectin column. One of the glycopeptides was successfully identified in the C. elegans genome database. Finally, for determination of Kd between glycopeptides and lectins, a recently reinforced frontal affinity chromatography (FAC) is proposed as an alternative to define glycan structures in place of determining every covalent structure.