Relationships among Catalytic Activity, Structural Flexibility, and Conformational Stability as Deduced from the Analysis of Mesophilic–Thermophilic Enzyme Pairs and Protein Engineering Studies

Introduction .................................................................................................................................. 25 Global and Local Probing of Structural Flexibility Correlated with Enzymatic Activity

and Thermal Stability ....................................................................................................... 26 Enzyme Engineering to Increase Stability or Catalytic Activity ................................................ 30

Rational Design ................................................................................................................ 30 Directed Evolution ............................................................................................................ 30

Conclusions .................................................................................................................................. 34 References .................................................................................................................................... 35

Naturally occurring enzymes must be stable to maintain their native structures even under unfavorable circumstances, for example at elevated temperatures or in the presence of harsh chemical conditions. On the other hand, enzymes also need to be suf ciently exible to perform their various catalytic activities. As a consequence, conformational stability may have been partially sacri ced for functional reasons during the evolution of enzymes. This idea has been supported by the generation of active site substitutions that resulted in stabilized enzymes with reduced activities [1-5].