Specificity of binding of three soluble rat lung lectins to substituted and unsubstituted mammalian beta-galactosides.
Binding of a series of mammalian glycoconjugates to three soluble rat lung lectins was determined with a quantitative assay. The three lectins, RL-14.5, RL-18, and RL-29, had a similar apparent affinity for lactose and associated with the same critical determinants, which included positions 4 and 6 of Gal and part of Glc. Derivatization at position 3 of Glc in lactose markedly reduced reactivity with the three lectins. For RL-14.5 and RL-29 the determinant extended specifically to the 3-hydroxyl of Glc which must be equatorial. In contrast, the stereochemical requirements for RL-18 were less specific, and Gal beta 1-3GalNAc bound as well as lactose. For RL-29 activity was markedly enhanced by GalNAc alpha 1-3 substitution on Gal, a modification which had little effect with RL-18 and inhibited binding to RL-14.5. Combinations of these residues in larger oligosaccharides and glycopeptides did not substantially enhance binding above that which might be expected from the sum of the constituent beta-galactoside residues. Although these lectins showed overlapping specificities, their binding properties are sufficiently different to suggest selective interactions with naturally occurring mammalian glycoconjugates.
D000818:Animals; D001665:Binding Sites; D005697:Galactosides / Q000378:metabolism* / Q000494:pharmacology; D006027:Glycosides / Q000378:metabolism*; D007457:Iodine Radioisotopes; D007553:Isotope Labeling; D007785:Lactose / Q000378:metabolism; D037102:Lectins / Q000302:isolation & purification / Q000378:metabolism*; D008168:Lung / Q000032:analysis*; D008968:Molecular Conformation; D051381:Rats; D013329:Structure-Activity Relationship
D005697:Galactosides; D006027:Glycosides; D007457:Iodine Radioisotopes; D037102:Lectins; C007816:beta-galactoside; D007785:Lactose