The binding modes of maltose binding protein with different ligands studied by NMR /

Maltose Binding Protein (MBP) of Escherichia Coli, a kind of periplasmic protein, can bind its ligands interacting predominantly either with their anomeric end (end-on binding) or with the middle of the maltodextrin chain (middle binding). Using NMR spectroscopy, we have studied the modes by which maltose, linear maltodextrin and some derivatives like $ beta$-cyclodextrin bind to MBP. 1D proton difference spectra and 2D HSQC proton-nitrogen correlation spectra were acquired of MBP in the presence of different ligands. Spectra with linear maltodextrins showed many common features and were distinctly different from those of MBP with $ beta$-cyclodextrin. 2D HSQC spectra suggest further that MBP- $ beta$-cyclodextrin adopts an open form conformation similar to that of ligand free MBP because of the surprisingly similarity of their spectra. Ligands such as $ beta$-cyclodextrin, can not be transported into the cyto-plasm but have high affinity for MBP, multiple $ alpha$(1-4) linkages and no reducing end. These ligands bind to MBP mainly by the middle binding mode. This suggests that this mode determines high affinity binding of ligand to MBP, but doesn't produce a physiologically active complex