Exoglycosidases and lectins as sequencing approaches of salivary gland oligosaccharides.

This review was focused on the salivary gland oligosaccharide chains studied by lectin histochemistry combined with exoglycosidase digestion. Glycoconjugates play an important role in many biofunctions and, generally, salivary mucins, which consist of numerous oligosaccharide chains attached at closely spaced intervals to a peptide backbone, serve as lubricants and protective agents, but in many instances we are ignorant about the role of biochemically identified oligosaccharides. Lectin histochemistry represents the greatest analytic tool to study carbohydrates in situ; in addition, there is availability of selective enzymes, so glycosidase degradation is useful to both investigate the structure of a given oligosaccharide and verify the influence of neighbouring sugars on the affinity towards the respective specific lectins. Using stepwise digestion of samples, followed by lectin labelling, the structure of terminal short oligosaccharides with blood-group activity was also elucidated. Additional histochemical methodologies were developed to establish the presence of acetylated groups in sialic acid residues, and the position of the linkage to the underlying monosaccharide. Sequencing approaches by exoglycosidases and lectins were also seen to be particularly useful when substantial differences did not emerge in lectin affinity, glycoconjugate composition and complex carbohydrate cytochemistry.