Carbohydrate structural units in glycosphingolipids as receptors for gal and GalNAc reactive lectins

Glycosphingolipids (GSLs) contain many carbohydrate epitopes or crypto-glycotopes for Gal and GalNAc reactive lectins. Many of them are in the nervous system and function as important receptors in various life processes. During the past two decades, 11 mammalian structural units have been used to express the binding domain of applied lectins. They are: F, GalNAcalpha1 --> 3GalNAc; A, GalNAcalpha1 --> 3Gal; T, Galbeta1 --> 3GalNAc; I, Galbeta1 --> 3GlcNAc; II, Galbeta1 --> 4GlcNAc; B, Galalpha1 --> 3Gal; E, Galalpha1 --> 4Gal; L, Galbeta1 --> 4Glc; P, GalNAcbeta1 --> 3Gal; S, GalNAcbeta1 --> 4Gal, and Tn, GalNAcalpha1 --> Ser(Thr). Although 10 of them occur in GSLs, only 3 (L-beta, S-beta, and T-beta) are found in human brain, and 2 (L-beta and IIbeta) are present in the inner structures of human blood group active GSLs. In the families of gangliosides, L-beta and IIbeta represent 55% of the total structural units, while the other three units (T-beta, P-alpha, and S-beta) constitute the rest. To facilitate the selection of lectins that could serve as structural probes, the carbohydrate binding specificities of Gal/GalNAc reactive lectins have been classified according to their highest affinity for the structural units and their binding properties expressed by decreasing order of reactivity. Hence, the binding relation between GSLs and Gal/GalNAc specific lectins can be established.