Seminar

Glycans by NMR: structure and molecular recognition

Ana Ardá, PhD

Carbohydrates (or sugars, or glycans) are key elements in Nature. Their molecular recognition by specific receptors is a fundamental step in many biological events, such as infections, inflammation, fertilization, cell adhesion, and others. The term Sugar Code was coined to describe how these recognition processes translate sugar encoded information into cellular responses. From a chemical structural point of view, carbohydrates are challenging: opposite to proteins and nucleic acids they are not biosynthesize in a template-driven process, they can be assembled through different linkages, and present different degrees of flexibility. In our group we try characterize the complex structural world of carbohydrates and to disclose the key structural elements that govern their molecular recognition by receptors, by using mainly Nuclear Magnetic Resonance (NMR). Our studies emphasize that the so called Sugar Code is not a univocal code based exclusively on epitope, and that assumed selectivities and specificities based on macroscopic techniques and on model systems (short oligosaccharides) might change depending on epitope presentation, remote chemical modifications, or receptor´s oligomeric state. The structural complexity of carbohydrates is generated through the glycosylation reaction. The intermediates formed in this reaction are the glycosyl oxocarbenium ions whose structure governs the stereochemical outcome of the products. However, due to their short-live nature they had not been isolated so far. Recently, we have been able for the first time to isolate and structurally characterize these species in solution.