Binding characteristics of galactoside-binding lectin (galaptin) from human spleen.
Binding characteristics of human spleen soluble galactoside-binding protein (galaptin) were studied using simple galactosides, galactose-terminated disaccharides, cluster glycosides containing up to 6 terminal lactosyl residues, bovine serum albumin derivatives containing 7 to 40 lactosyl residues, desialylated serum glycoproteins, and glycopeptides derived thereof as inhibitors in a newly developed binding assay. In this assay, aminohexyl lactoside was attached to divinyl sulfone-activated Sepharose, which was then used to bind 125I-galaptin. Similarly derivatized Sepharose containing mannoside served as a control. The assay is sensitive, maintains linearity in the concentration range of 125I-galaptin tested, and has very low nonspecific binding. The following new findings were made. 1) All the alpha-D-galactopyranosides with non-sugar aglycon were better inhibitors than the corresponding beta-D-galactopyranoside. 2) The S-galactosides were better inhibitors than the corresponding O-galactosides, regardless of the anomeric configuration. 3) Many Gal beta 1-4- and Gal beta 1-3-linked disaccharides were tested. Although the galaptin did not appear to recognize N-acetylglucosamine as a monosaccharide, the presence of this sugar penultimate to galactose increased the binding affinity by as much as 500-fold, as was the case for N-acetyllactosamine. Of a particular importance is the presence of an equatorial 3-OH group on this sugar. We synthesized the 3-deoxy derivative of N-acetyllactosamine and found that it had 50-fold lower binding affinity compared to N-acetyllactosamine. 4) The binding sites of this lectin do not seem to be operating in a cooperative fashion, since synthetic lactose-containing divalent ligands with various inter-galactose distances did not increase the binding affinity significantly.
Lee
R T
RT
Department of Biology, Johns Hopkins University, Baltimore, Maryland 21218.
Ichikawa
Y
Y
Allen
H J
HJ
Lee
Y C
YC
D001665:Binding Sites; D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D004187:Disaccharides / Q000378:metabolism / Q000494:pharmacology; D005690:Galactose / Q000494:pharmacology; D005697:Galactosides / Q000378:metabolism / Q000494:pharmacology; D037161:Galectins; D006020:Glycopeptides / Q000378:metabolism / Q000494:pharmacology; D006023:Glycoproteins / Q000378:metabolism / Q000494:pharmacology; D006027:Glycosides / Q000378:metabolism / Q000494:pharmacology; D006388:Hemagglutinins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007785:Lactose / Q000378:metabolism / Q000494:pharmacology; D008969:Molecular Sequence Data; D015394:Molecular Structure; D012710:Serum Albumin, Bovine / Q000378:metabolism / Q000494:pharmacology; D013154:Spleen / Q000032:analysis*; D013329:Structure-Activity Relationship
D004187:Disaccharides; D005697:Galactosides; D037161:Galectins; D006020:Glycopeptides; D006023:Glycoproteins; D006027:Glycosides; D006388:Hemagglutinins; C008245:lactosides; D012710:Serum Albumin, Bovine; D007785:Lactose; D005690:Galactose