Thermal Stability of Onconase and Some Mutant Forms

Onconase is a small globular protein of the pancreatic ribonuclease superfamily. It is an important molecule because it possesses a selective antitumor activity. The interesting finding is that onconase has a high thermal stability, with a denaturation temperature close to 90d`C at p^H 6.0. A detailed comparison between the tertiary structures of onconase and bovine pancreatic ribonuclease has been accomplished in order to identify the molecular determinants of the high stability. The results of differential scanning calorimetry measurements confirm that the mutant forms of onconase, designed to be less stable than the parent enzyme, exhibit lower denaturation temperatures. In particular, the disulfide bridge at the C-terminus of onconase seems to play a pivotal role in stability.