The chemical mapping of the regions of H-type 2 human blood group-related trisaccharide (Fuc alpha (1-2)Gal beta (1-4)GlcNAc beta Me) that are recognized by three different lectins, the so-called epitopes, are reviewed together with an account of how and why oligosaccharides form specific complexes with proteins as presently viewed in this laboratory. The occasion is used to report the synthesis of the various mono-O-methyl derivatives of the above trisaccharide that were used in these investigations. Also, Fuc alpha (1-2)Gal beta (1-4)Xyl beta Me was synthesized in order to examine whether or not the hydroxymethyl group of the GlcNAc residue participates in the binding reaction.

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The winged bean acidic lectin (WBA 11) binds the H-type 2 human blood group related trisaccharide (a-L-Fuc-(lc + 2b)-P-D-Gal-(1 b + 4a)-P-D-GlcNAc-OMe, 1). Interactions that importantly contribute to the specificity of the complex formation are provided by CH2-6b, OH-4b, OH-3b, and OH-2c of 1. On the basis of the relative activities of the monodeoxy and mono-0-methyl derivatives of 1, the hydroxyl groups at the 3a, 6a, and 4c positions become located at the periphery of the combining site, whereas the CH30-la, NHAc-2a, and CH3-5c groups are more remote from the protein surface and fully exposed to bulk water. Whereas the WBA I1 lectin marginally recognizes the H- (24) is bound 3.4 times more strongly than 1. This and other results, which are related to changes in interaction between the ligand and the apron of the combining site, are attributed to changes in hydration that lead to enthalpy~ntropy compensation. In certain cases, the interactions are found to stabilize the complex. [Traduit par la rCdaction]

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