Mapping the Conformational Stability of Maltose Binding Protein at the Residue Scale Using Nuclear Magnetic Resonance Hydrogen Exchange Experiments

Being able to differentiate local fluctuations from global folding–unfolding dynamics of a protein is of major interest for improving our understanding of structure–function determinants. The maltose binding protein (MBP), a protein that belongs to the maltose transport system, has a structure composed of two globular domains separated by a rigid-body “hinge bending”. Here we determined, by using hydrogen exchange (HX) nuclear magnetic resonance experiments, the apparent stabilization free energies of 101 residues of MBP bound to β-cyclodextrin (MBP−βCD) under native conditions. We observed that the last helix of MBP (helix α14) has a lower protection factor than the rest of the protein. Further, HX experiments were performed using guanidine hydrochloride under subdenaturing conditions to discriminate between local fluctuations and global unfolding events and to determine the MBP−βCD energy landscape. The results show that helix α4 and a part of helices α5 and α6 are clearly grouped into a subdenaturing f...