An NMR study of ligand binding by maltodextrin binding protein

Proton NMR spectra of maltodextrin binding protein from Escherichia coli we re used to monitor conformational changes that accompany ligand binding. Ch emical shift changes associated with the binding of different maltodextrins to maltodextrin binding protein were studied using one-dimensional differe nce spectra. Line-shape analysis of an isolated upfield methyl resonance wa s used to measure the kinetics of maltose binding at several temperatures. Maltose and linear maltodextrins caused similar changes to the upfield prot ein spectrum with no detectable differences between alpha and beta sugar an omers. Binding of a cyclic ligand, P-cyclodextrin, caused smaller chemical shift changes than binding of linear maltodextrins. Two maltodextrin deriva tives were also studied. Both maltohexaitol and maltohexanoic acid gave one -dimensional difference spectra that were intermediate between those of lin ear maltodextrins and beta-cyclodextrin. The methyl resonances at -1 and -0 .35 ppm were assigned to leucine 160 on the basis of homonuclear COSY and T OCSY experiments and theoretical chemical shift calculations using the X-ra y crystal structure of maltodextrin binding protein.