On the stringent requirement of mannosyl substitution in mannooligosaccharides for the recognition by garlic (Allium sativum) lectin -: A surface plasmon resonance study

The kinetics of the binding of mannooligo saccharides 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 alpha -1,2-linked mannose residues. An increase in binding propensity can be directly correlated to the addition of alpha -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-alpha = 1.2 x 10(6) M-1 at 25 degreesC). An analysis of these data reveals that the alpha -1,2-linked terminal mannose on the (alpha -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 x 10(4) M-1 s(-1) and 4.9 x 10(-2) s(-1), respectively, at 25 degreesC. 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.