LIGAND-INDUCED PERTURBATIONS IN URTICA-DIOICA AGGLUTININ

The binding of the trisaccharide, N,N',N''-triacetylchitotriose, to Ur tica dioica agglutinin (UDA) was investigated using H-1 NMR spectrosco py, UDA is a small antiviral plant lectin containing two homologous 43 -amino acid domains. Carbohydrate-induced perturbations occur in one d omain of UDA at trisaccharide concentrations below equimolar. Residues in the second domain are shifted at higher carbohydrate concentration s. This data confirms the presence of two binding sites of nonidentica l affinities per UDA monomer. Qualitative analysis of the 2D NOESY spe ctra indicates that UDA contains two short stretches of antiparallel b eta-sheet. The H-1 resonance assignments for both antiparallel beta-sh eet sequences have been completed and there is one beta-stretch per do main. A number of these beta-sheet residues are perturbed in the prese nce of carbohydrate.