Thermodynamic analysis of ligand binding to winged bean (Psophocarpus tetragonolobus) acidic agglutinin reveals its specificity for terminally monofucosylated H-reactive sugars.
The sugar-specific binding of N-dansylgalactosamine to WBA II (n = 2; Ka = 5.6 x 10(3) M-1; delta H = -21 kJ.mol-1; delta S = -21.3 J.mol-1.K-1) was utilized in substitution titrations for evaluating the association constants for the interaction of sugars with the lectin. An axial hydroxyl at C-4 and equatorial hydroxyls at C-3 and C-6 as in D-galacto configuration are crucial for binding. Both axial and equatorial hydroxyls are tolerated at C-2. Conformationally akin disaccharides such as lactose, N-acetyllactosamine, Gal beta 1-3GlcNAc, and Gal beta 1-3GalNAc show similar affinities. 2'-Fucosyllactose and H-disaccharide display 146 and 13 times stronger affinity over lactose and galactose, yet fucose by itself is devoid of activity. An interesting feature, noted for the first time, in protein-sugar interactions is the positive entropy change for the binding of 2'-fucosyllactose, suggesting that nonpolar interactions play an important role in stabilization of the lectin-sugar complex. 3-Fucosyllactose, lactodifucotetraose, lacto-N-fucopentaose II and III are inactive, whereas lacto-N-fucopentaose I has 14-fold lower affinity as compared with 2'-fucosyllactose. Conformational analysis indicates that the substitution at subterminal glucose or GlcNAc by L-fucose in either alpha 1-3 or alpha 1-4 linkage leads to its projection so as to sterically hinder the access of 3'-fucosyllactose, lactodifucotetraose, and lacto-N-fucopentaose II and III to the binding site of winged bean agglutinin II. Similarly the projection of alpha 1-3 linked Gal/GalNAc also leads to steric hindrance and hence prevents the binding of blood group A and B reactive sugars. Considering its unique specificity winged bean agglutinin II should be useful in the isolation and characterization of terminally monofucosylated H-reactive oligosaccharides from those that are difucosylated or internally fucosylated.
Acharya
S
S
Molecular Biophysics Unit, Indian Institute of Science, Bangalore.
Patanjali
S R
SR
Sajjan
S U
SU
Gopalakrishnan
B
B
Surolia
A
A
D002151:Calorimetry; D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D002241:Carbohydrates; D003619:Dansyl Compounds; D004187:Disaccharides; D005456:Fluorescent Dyes; D005643:Fucose; D005688:Galactosamine / Q000031:analogs & derivatives; D007700:Kinetics; D037102:Lectins / Q000302:isolation & purification; D008024:Ligands; D008433:Mathematics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D037121:Plant Lectins; D011485:Protein Binding; D011487:Protein Conformation; D013050:Spectrometry, Fluorescence; D013816:Thermodynamics
D002241:Carbohydrates; D003619:Dansyl Compounds; D004187:Disaccharides; D005456:Fluorescent Dyes; D037102:Lectins; D008024:Ligands; D037121:Plant Lectins; C049304:winged bean lectin; D005643:Fucose; D005688:Galactosamine; C041456:dansylgalactosamine