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 i nteraction of the bound lectin immobilized on the sensor chip with a select ed group of high mannose oligosaccharides was monitored in real time with t he change in response units. This investigation corroborates our earlier st udy about the special preference of garlic lectin for terminal alpha -1,2-l inked mannose residues. An increase in binding propensity can be directly c orrelated to the addition of alpha -1,2-linked mannose to the mannooligosac charide at its nonreducing end. Mannononase glycopeptide (Man(9)GlcNAc(2)As n), 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 reveal s 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 le ctin, The association (k(1)) and dissociation rate constants (k(-1)) for th e 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 d ramatically so for Man(8) and Man(9) derivatives, (k-1) decreases relativel y much less gradually from Man(3) to Man(9) structures. An unprecedented in crease 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.