Complex Carbohydrate Research Center, University of Geogia, Athens, Georgia
A major obstacle to advances in glycobiology is the lack of pure and structurally well-defined carbohydrates and glycoconjugates. We have developed a chemo-enzymatic methodology that makes it possible to prepare libraries of highly complex asymmetrically substituted glycans. A key feature of the technology is the use of a core pentasaccharide that at key branching positions is modified by the orthogonal protecting groups to allow selective attachment of unique saccharide structures by chemical glycosylation methodology. The appendages were selected in such a way that the antenna of the resulting compounds can be uniquely extended by glycosyl transferases to give large numbers of highly asymmetrical substituted multi-antennary glycans. The power of the methodology has been demonstrated by the preparation of a tri-antennary oligosaccharide that can inhibit binding of spermatozoan to the zona pellucida of human oocytes. Furthermore, a series of symmetrical and asymmetrical oligosaccharides have been prepared that were printed as microarrays and screened for binding to lectins and influenza-virus hemagglutinins. These studies have demonstrated that glycan recognition is modulated by presentation of minimal epitopes in the context of complex N-glycans.
