Binding and Precipitating Activities of Lotus tetragonolobus Isolectins with L-Fucosyl Oligosaccharides. Formation of Unique Homogeneous Cross-Linked Lattices Observed by Electron Microscopy

We have recently observed that certain asparagine-linked oligosaccharides are multivalent and capable of binding and precipitating with the D-mannose-specific lectin concanavalin A [cf. Bhattacharyya, L., & Brewer, C. F. (1989) Eur. J. Biochem. 178, 721-726] and with a variety of D-galactose-specific lectins [Bhattacharyya, L., Haraldsson, M., & Brewer, C. F. (1988) Biochemistry 27, 1034-1041], In the present study, we have examined the binding and precipitating activities of a variety of mono- and biantennary L-fucosyl oligosaccharides with three L-fucose-specific isolectins from Lotus tetragonolobus, LTL-A, LTL-B, and LTL-C. The results show that certain difucosyl biantennary oligosaccharides are capable of cross-linking and precipitating with tetrameric isolectins, LTL-A and LTL-C., but not with dimeric isolectin, LTL-B. Quantitative precipitation analyses show that biantennary oligosaccharides containing the Lewis^x antigen (or type 2 chain of Lewis³), Galβ (1-4)[Fucα(1-3)]GlcNAc, at the nonreducing terminus of each arm are bivalent ligands. However, a biantennary oligosaccharide containing a Lewis^x determinant on one arm and a type 2 chain of blood group H(0) determinant, Fucα(1-2)Gal/3(1-4)GlcNAc, on the other arm and a monoantennary oligosaccharide containing two fucose residues (analogue of the Lewis^y antigen) bind but do not precipitate with the isolectins, indicating that the positions and linkage of fucose residues are critical for cross-linking. The presence or absence of the galactose residues in the Le^x antigenic determinant(s) of the oligosaccharides does not affect the affinities of the carbohydrates for the isolectins but has a strong influence on the temperature sensitivity and kinetics of the precipitation reactions with LTL-A and LTL-C. On the other hand, the presence of the α(l-3) fucose residues in the oligosaccharides with terminal β(1-4) galactose residues eliminates binding of the carbohydrates to certain galactose-specific lectins. The precipitates formed between the oligosaccharides and LTL-A and LTL-C have also been examined by electron microscopy. The precipitates of LTL-A show a distinct lattice pattern for each oligosaccharide, indicating the presence of long-range order and well-defined geometry in each cross-linked complex. However, the precipitates of LTL-C show no pattern. The precipitates of LTL-A formed in the presence of a mixture of two oligosaccharides show patterns characteristic of one or the other oligosaccharide depending on the relative concentrations of the carbohydrates. Similar findings were also obtained with the precipitates of binary mixtures of LTL-A and LTL-C with one oligosaccharide. These studies thus demonstrate the formation of distinct homogeneous cross-linked lattices between LTL-A and three bivalent oligosaccharides, as well as different stabilities for the cross-linked lattices of LTL-A and LTL-C with a given oligosaccharide. The results are discussed in terms of the structure-function properties of multivalent oligosaccharides and lectins.