Compatible solutes as protectants for zymogens against proteolysis

Compatible solutes are small organic osmoprotectants that have the capability to stabilize proteins. In coupled assays, the effect of the solutes ectoine, hydroxyectoine and betaine on the activation of the zymogens trypsinogen and chymotrypsinogen, catalyzed by enteropeptidase and trypsin, respectively, was studied. To different extents, all solutes protected the zymogens against activation. Ectoine (800 mM) was the most potent solute in reducing the formation of trypsin to 4% of the control value and of chymotrypsin to 23%. In separate experiments, the ability of the solutes to preserve proteolytic activity during incubation was investigated. After 4 h, trypsin and chymotrypsin completely lost their activity, but in the presence of ectoine, approximately 50% residual activity was maintained. It is proposed that a conformational shift of the protein towards folded, native-like states induced by preferential exclusion of the solute is responsible for the stabilizing and chaperone-like effects.