Rational protein modification leading to resistance of enzymes to TiO2-UV irradiation-induced inactivation.

Photoexcited TiO2 degrades biomolecules such as nucleic acids, cell membrane proteins, and enzymes. Stabilization of enzyme activity against the deactivation caused by the combination of TiO2-UV is essential if we are to develop novel hybrid materials exhibiting photocatalytic and biocatalytic activities useful for decontamination applications. In this paper we describe the stabilization of a model enzyme, chymotrypsin, against TiO2-UV-induced deactivation by conjugating the enzyme with UV-absorbing, carboxyl-terminated oligo[2-[3-(2H-benzotriazol-2-yl)-4-hydroxyphenyl]ethyl methacrylate] [oligo(HBMA)-COOH]. Chymotrypsin was completely deactivated within 3 h, whereas the chymotrypsin-oligo(HBMA) conjugate retained > 50% activity even after 5 h of exposure to TiO2-UV (lambdamax 365 nm). The degree of enzyme stabilization induced by the conjugated UV absorber was 2-fold higher than that from the equivalent number of conjugated PEG chains. Spectroscopic characterizations revealed that chymotrypsin-oligo(HBMA) absorbs UV light and initially resists photoexcitation of TiO2. Modified chymotrypsin also exhibited resistance to changes in the secondary structure during the deactivation. This method of stabilizing enzymes against photodegradation could be also useful in photolithographic enzyme immobilizations for sensors and arrays or for stabilization of any UV-sensitive protein.