Engineering a hyperstable enzyme by manipulation of early steps in the unfolding process

Protein engineering experiments have recently yielded hyperstable variants of the thermolysin-like protease from Bacillus stearothermophilus (TLP-ste). These variants contain mutations suggested by comparison of TLP-ste with its more thermostable counterpart thermolysin, as well as rationally designed mutations. The key to the successful stabilization strategy was the identification of a weak region that is involved in early unfolding events (unfolding region). Mutations in this region had large effects on stability, whereas mutations in other parts of the protein generally had minor effects. The mutational strategies that were used as well as characteristics of the engineered hyperstable biocatalysts are reviewed below.