Expression of binding properties of Gal/GalNAc reactive lectins by mammalian glycotopes

Abstract

Expression of the binding properties of Gal/GalNAc specific lectins, based on the affinity of decreasing order of mammalian glycotopes (determinants) rather than monosaccharide inhibition pattern, is probably one of the best ways to express carbohydrate specifity and should facilitate the selection of lectins as structural probes for studying mammalian glycobiology. Eleven mammalian structural units have been selected to express the binding domain of applied lectins. They are: 1. F, GalNAcα1→3GalNAc; 2. A, GalNAcα1→3Gal; 3. T, Galβ1→3GalNAc; 4. I, Galβ1→3GlcNAc; 5. II, Galβ1→4GlcNAc; 6. B, Galα1→3Gal; 7. E, Galα1→4Gal; 8. L, Galβ1→4Glc; 9. P, GalNAcβ1→3Gal; 10. S, GalNAcβ1→4Gal and 11. Tn, GalNAcα1→Ser (Thr) of the peptide chain. Thus, the carbohydrate specificity of Gal/GalNAc reactive lectins can be divided into classes according to their highest affinity for the above disaccharides and/or Tn residue. Examples of the binding properties of these lectins can be demonstrated by Ricinus communis agglutinin (RCA1), grouped as II specific lectin and its binding property is II > I > B > T; Abrus precatorius agglutinin (APA), classified as T and its carbohydrate specificity is T > I/II > E > B > Tn; Artocarpus integrifolia (jacalin, AIL), as T/Tn specific and its binding reactivity is T > Tn ≫ I (II) and Geodia cydonium (GCL), as F/A specific, and with affinity for F > Ah, [ GalNAcα1→3(LFucα1→2)Gal] ≫ I > L. Due to the multiple reactivity of lectins toward mammalian glycotopes, the possible existence of different combining sites or subsites in the same molecule has to be examined, and the differential binding properties of these combining sites (if any) have to be characterized. To establish the relationship among the amino acid sequences of the combining sites of plant lectins and mammalian glycotopes should be an important direction to be addressed in lectinology.