We have used UV absorbance spectroscopy to study the binding of linear and circular maltodextrins to maltose-binding protein (MBP). Titrations with maltose yield three ??? points in the difference spectrum of MBP, consistent with two protein conformations: ligand-free and ligand-bound. In contrast, titrations with maltotetraose reveal three conformation: ligand-free, a low-affinity liganded state, and a high affinity liganded state. These results confirm and extend the results from tritium NMR spectroscopy, namely, that MBP can bind maltodextrin either by the sugar's anomeric end (high affinity) or by the middle of the maltodextrin chain flow affinity.
