Interactions of concanavalin A with glycoproteins: formation of homogeneous glycoprotein-lectin cross-linked complexes in mixed precipitation systems

We have previously demonstrated that the interactions between branched chain oligosaccharides and glycopeptides isolated from glycoproteins and glycolipids with specific lectins lead to the formation of homopolymeric carbohydrate-protein cross-linked complexes, even in the presence of mixtures of the carbohydrates or lectins [cf. Bhattacharyya, L., Fant, J., Lonn, H., & Brewer, C. F. (1990) Biochemistry 29, 7523-7530]. Recently, we have shown that highly ordered cross-linked lattices are formed between the tetrameric glycoprotein soybean agglutinin (SBA), which possesses a Man9 oligomannose chain per monomer, and the Glc/Man-specific plant lectin concanavalin A (Con A) [Khan, M. I., Mandal, D. K., & Brewer, C. F. (1991) Carbohydr. Res. 213, 69-77]. Using radiolabeling and quantitative precipitation techniques, we show in the present study that Con A binds and forms unique cross-linked complexes with four different glycoproteins having different numbers and types of carbohydrate chains as well as different quaternary structures. The glycoproteins include quail ovalbumin, Lotus tetragonolobus isolectin A (LTL-A), Erythrina cristagalli lectin (ECL), and Erythrina corallodendron lectin (EcorL). The results show that a preparation of quail ovalbumin containing either one Man7 or Man8 oligomannose chain per molecule forms a 1:2 cross-linked complex with tetrameric Con A, thereby demonstrating bivalency of the single carbohydrate chain(s) on the glycoprotein. Tetrameric LTL-A and dimeric ECL, which possess two xylose-containing carbohydrate chains per monomer, both form 1:2 and 1:1 cross-linked complexes (per monomer) of glycoprotein to lectin, depending on their relative ratios in solution. However, dimeric EcoRI, which has the same carbohydrate structure and number of chains as ECL, forms only a 1:2 cross-linked complex with tetrameric Con A. Quail ovalbumin does not precipitate with dimeric acetyl- or succinyl-Con A, while LTL-A, ECL, and EcorL form 1:2 complexes with acetyl-Con A but fail to precipitate with succinyl-con A. Mixed quantitative precipitation studies show that Con A forms the same unique stoichiometry cross-linked complexes with the above glycoproteins including SBA in the presence of binary mixtures of the glycoproteins. These results provide evidence that each glycoprotein forms a unique homopolymeric cross-linked lattice(s) with Con A which excludes the lattices of other glycoproteins. The present findings thus represent a new source of binding specificity between lectins and glycoproteins, namely, the formation of homogeneous aggregated complexes. The results are discussed in terms of the possible biological recognition properties of lectins and glycoconjugates as receptors.