Stabilization mechanism of MPEG modified trypsin based on thermal inactivation kinetic analysis and molecular modeling computation

Thermal inactivation kinetic analysis and molecular modeling computation were jointly utilized to illuminate the detailed stabilization mechanism of trypsin caused by methoxypolyethylene glycol (MPEG) modification. First, trypsin was modified by MPEG (molecular mass 350 Da) to enhance its thermal stability. As expected, the modified trypsin was more stable against temperature than the native form. Second, a new kinetic model, which has the ability of taking the thermal denaturation and autolysis effects of proteases into account, was established and used to analyze the thermal inactivation process of the native and modified trypsin. The kinetic analysis showed that the increased thermal stability of MPEG modified trypsin is the joint result of a reduction in autolysis and a decrease in thermal denaturation. Finally, the molecular modeling technique was also employed to calculate some structural information change, i.e. solvent accessible surface, intramolecular hydrogen bond and root mean square fluctuation, between the native and modified trypsin. The results of molecular modeling computation demonstrated that (i) the steric hindrance caused by MPEG chain would result in the decreased rate of autolysis, (ii) the decreased rate of thermal denaturation should be ascribed to the increased number of hydrogen bond, not the result of the increased molecular rigidity.