Sialic acids structure-analysis-metabolism-occurrence-recognition.

Sialic acids are commonly positioned at non-reducing termini of complex carbohydrates. Steady refinements of analytical techniques have enabled detailed mapping of the complexity of sialic acids, unravelling a number of possibilities for substitutions. These developments have aided the description of the required enzymatic activities. In view of the physiological significance of this intriguing extent of variability of one sugar unit, the assumption that distinct types of sialic acids can serve as ligands in recognitive interactions is gaining support. It is reinforced by the discovery of several classes of mammalian lectins that bind sialo-glycoconjugates. Notably, an often encountered modification of sialic acids, namely O-acetylation, can be considered as a modulatory signal in recognition, either serving as contact point or masking a ligand structure. The increased knowledge of the physiological roles of sialic acids, for example in selectin-mediated leukocyte recruitment to sites of inflammation or in influenza virus propagation, even points to clinical applications. This perspective has led the field from the inherently descriptive beginning to technically sophisticated attempts for deliberate drug design.