Conformational Analysis of Biantennary Glycopeptides with a Resonance Energy Transfer Technique

The carbohydrate components in glycoprotein receptors, antibodies, enzymes, toxins, and hormones are increasingly gaining attention as biological recognition signals (1 ,2 ). It is, therefore, important to study the conformation of oligosaccharides in solution to better understand the mechanism of carbohydrate-protein interactions. X-ray diffraction (3 ), electron spin resonance (4 ), computer molecular modeling (5 ), and nuclear magnetic resonance (NMR) have been used to determine oligosaccharide conformation. Proton NMR has played a major role in determination of the solution conformation of oligosaccharides or glycopeptides by measuring the nuclear. Overhauser effect (NOE) that is suitable for the distance of 2–5� (6 –8 ) (see Chapter 1 ). However, in measuring the long range (10–50�) distances in biological systems, resonance energy transfer measurements are more suitable and more sensitive tools (only nanomole-range samples are required) (9 ,10 ). In order to apply resonance energy transfer techniques to conformational studies of complex type branched oligosaccharides, fluorescence donor and accepter molecules must be introduced at specific sites on different branches. Using such an approach, Rice et al. (11 ) were able to characterize conformations of triantennary glycopeptides in solution by using time-resolved resonance energy transfer. This technique was extended to study the solution conformation of biantennary glycopeptides. Examples of modification of biantennary glycopeptides with donor and accepter probes and measurement of energy transfer are described in this chapter.