Ligand-induced structural changes to maltodextrin-binding protein as studied by solution NMR spectroscopy

Solution NMR studies on the physiologically relevant ligand-free and maltot riose-bound states of maltodextrin-binding protein (MBP) are presented. Tog ether with existing data on MBP in complex with beta -cyclodextrin (non-phy siological, inactive ligand), these new results provide valuable informatio n on changes in local structure, dynamics and global fold that occur upon L igand binding to this two-domain protein. By measuring a large number of di fferent one-bond residual dipolar couplings, the domain conformations, crit ical for biological function, were investigated for all three states of MBP . Structural models of the solution conformation of MBP in a number of diff erent forms were generated from the experimental dipolar coupling data and X-ray crystal structures using a quasi-rigid-body domain orientation algori thm implemented in the structure calculation program CNS. Excellent agreeme nt between relative domain orientations in Ligand-free and maltotriose-boun d solution conformations and the corresponding crystal structures is observ ed. These results are in contrast to those obtained for the MBP/beta -cyclo dextrin complex where the solution state is found to be similar to 10 degre es more closed than the crystalline state. The present study highlights the utility of residual dipolar couplings for orienting protein domains or mac romolecules with respect to each other. (C) 2001 Academic Press.