The kinetics of the binding of mannooligosaccharides to the heterodimeric lectin from garlic bulbs was studied using surface plasmon resonance. The interaction of the bound lectin immobilized on the sensor chip with a selected group of high mannose oligosaccharides was monitored in real time with the change in response units. This investigation corroborates our earlier study about the special preference of garlic lectin for terminal ␣-1,2-linked mannose residues. An increase in binding propensity can be directly correlated to the addition of ␣-1,2-linked mannose to the mannooligosaccharide at its nonreducing end. Mannononase glycopeptide (Man 9 GlcNAc 2 Asn), the highest oligomer studied, exhibited the greatest binding affinity (K a ؍ 1.2 ؋ 10 6 M ؊1 at 25°C). An analysis of these data reveals that the ␣-1,2-linked terminal mannose on the ␣-1,6 arm is the critical determinant in the recognition of mannooligosaccharides by the lectin. The association (k 1 ) and dissociation rate constants (k ؊1 ) for the binding of Man 9 GlcNAc 2 Asn to Allium sativum agglutinin I are 6.1 ؋ 10 4 M ؊1 s ؊1 and 4.9 ؋ 10 ؊2 s ؊1 , respectively, at 25°C. Whereas k 1 increases progressively from Man 3 to Man 7 derivatives, and more dramatically so for Man 8 and Man 9 derivatives, k ؊1 decreases relatively much less gradually from Man 3 to Man 9 structures. An unprecedented increase in the association rate constant for interaction with Allium sativum agglutinin I with the structure of the oligosaccharide ligand constitutes a significant finding in protein-sugar recognition.The structurally and evolutionarily related monocot mannose-binding proteins comprise a superfamily of mannose-specific lectins. Amaryllidaceae, Alliaceae, Araceae, Orchidaceae, Iridaceae, and Liliaceae families have been shown to possess these bulb lectins (1). Among the unique features that set them apart from the Glc/Man/Gal-specific family of dicotyledonous legume lectins and the C-type mannose-binding animal lectins is their high degree of stereospecificity for mannose, so much so that they show no binding propensity even for its epimer, glucose, or the conformationally related analog, L-fucose. Their classification into the mannose-specific lectin family is corroborated by determination of the crystal structures of snowdrop (Galanthus nivalis) (2), daffodil (Narcissus pseudonarcissus) (3), bluebell (Scilla campanulata) (4), amaryllis (Hippeastrum hybrid) (5), and garlic (Allium sativum) lectin (6), representatives of the family of bulb lectins. Their subunits have been observed to possess a novel 3-fold symmetry having three fourstranded antiparallel -sheets arranged as three sides of a triangular prism, forming a 12-stranded -barrel referred to as the -prism II fold. These 12 strands are positioned perpendicular to the plane of symmetry, unlike the other known all--folds: -prism I (e.g. Jacalin; (7)) and the -trefoil (e.g. amaranthin; (8)) fold (6). The central region in the -barrel is stacked with conserved hydrophobic side chains, which stabilize th...
