MOLECULAR RECOGNITION .8. THE BINDING OF THE BETA-D-GALACTOPYRANOSYL RESIDUE OF THE LEWIS-B HUMAN-BLOOD GROUP DETERMINANT BY THE LECTIN-IV OF GRIFFONIA-SIMPLICIFOLIA AND BY A MONOCLONAL ANTI-LEWIS B-ANTIBODY - EVIDENCE FOR INTRAMOLECULAR HYDROGEN-BONDING

The 3b-deoxy, 4b-deoxy, 6b-deoxy, 6-deoxy-6b-fluoro, 6b-chloro-6b-deoxy, and the 5-des-hydroxymethyl derivatives of the Lewis b (.alpha.LFucd(1 .fwdarw. 2) .beta.DGalb(1 .fwdarw. 3) [.alpha.Fucc (1 .fwdarw. 4)].beta.DGlcNAca-OMe) human blood group determinant were synthesized in order to examine the involvement of the .beta.Dgal b unit in the binding of the Leb-OMe tetrasaccharide both by the lectin IV of Griffonia simplicifolia and a hybridoma monoclonal anti-Leb antibody. The replacement of the CH2OH-5b group by hydrogen resulted in very weak binding by both the proteins, but the 6b-deoxy derivative was bound nearly as strongly as the parent compound in the case of the lectin but nine times more strongly in the case of the antibody. The 6b-fluoride was slightly more strongly bound than the 6b-deoxy derivative by both the proteins. On the other hand, the 6b-chloride was bound three times more strongly by the lectin but three times more weakly by the antibody than the 6b-deoxy derivative. The thermodynamic parameters for the binding of the 6b-deoxy derivative by the lectin as compared to those for Lbb-OMe conformed that OH-6b interactions within the combining site of the complex. The results appear to require that for both proteins the CH2-OH-5b group becomes involved in nonpolar interactions within the combining site. It seems probable that OH-6b is accepted intramolecularly hydrogen bonded to 0-5b in the case of the lectin but to OH-4b in the case of the antibody. The involvement of OH-3b, OH-4b, and OH-4c as the key polar grouping for the binding of Leb-OMe by the lectin and of OH-3b and OH-2d in the case of the antibody was reported previously.