OLIGOSACCHARIDES - HOW CAN FLEXIBLE MOLECULES ACT AS SIGNALS

There is considerable evidence that the majority of oligosaccharides are flexible, that is, they exist in many different conformations. How, then, can they act effectively as recognition signals? There must be a mechanism to reduce this flexibility so that the high-affinity, high-specificity, binding characteristic of ''recognition'' phenomena can be achieved. Specific sets of molecular interactions at individual glycosylation sites are suggested to be responsible. Through such specific interactions, subsets of the total population of a given oligosaccharide could be capable of acting as recognition signals. Since a dominant role is played by interactions with the protein surface at the glycosylation site, we term this mechanism ''site-directed presentation''. The previously described phenomenon of ''site-directed processing'' is simply a special case of the more general site-directed presentation phenomenon. Possible molecular models for this phenomenon are reviewed and the experimental bases presented.