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

Abstract

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 α-1,2-linked mannose residues. An increase in binding propensity can be directly correlated to the addition of α-1,2-linked mannose to the mannooligosaccharide at its nonreducing end. Mannononase glycopeptide (Man₉GlcNAc₂Asn), the highest oligomer studied, exhibited the greatest binding affinity (K_a=1.2×10⁶ M⁻¹ at 25°C). An analysis of these data reveals that the α-1,2-linked terminal mannose on the α-1,6 arm is the critical determinant in the recognition of mannooligosaccharides by the lectin. The association (k₁) and dissociation rate constants (k₋₁) for the binding of Man₉GlcNAc₂Asn to Allium sativumagglutinin I are 6.1×10⁴ M⁻¹ s⁻¹ and 4.9×10⁻² s⁻¹, respectively, at 25°C. Whereas k₁ increases progressively from Man₃ to Man₇ derivatives, and more dramatically so for Man₈ and Man₉ derivatives, k₋₁ decreases relatively much less gradually from Man₃ to Man₉ 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.