Structural Basis for the Binding of Compatible Solutes by

Compatible solutes such as glycine betaine and pro-line betaine serve as protein stabilizers because of their preferential exclusion from protein surfaces. To use ex-tracellular sources of this class of compounds as osmo-, cryo-, or thermoprotectants, Bacteria and Archaea have developed high affinity uptake systems of the ATP-bind-ing cassette type. These transport systems require periplasmic- or extracellular-binding proteins that are able to bind the transported substance with high affin-ity. Therefore, binding proteins that bind compatible solutes have to avoid the exclusion of their ligands within the binding pocket. In the present study we ad-dressed the question to how compatible solutes can be effectively bound by a protein at temperatures around 83 °C as this is done by the ligand-binding protein Pro