Immobilization of urease enzyme on nanoceria modifies secondary and tertiary protein structures

Urease catalyzes the hydrolysis of urea to form ammonia and carbon dioxide. The increase in pH from the urease reaction causes a broad range of deleterious effects. Nanoceria (cerium oxide) possesses unique chemical properties under a redox reaction. This study investigated the synthesis of nanoceria via a hydrothermal method and determined its interaction with urease enzyme.

Transmission electron microscopy results showed a cubic-figured nanoceria with a size of ~15 nm. Urease was immobilized on nanoceria through adsorption. The maximum velocity (V_max) and Michaelis constant (K_m) of the free urease and urease immobilized on nanoceria decreased after interaction with nanoceria, and the Lineweaver-Burk plot showed an uncompetitive inhibition. The thermodynamic study of the adsorption process showed an endothermic reaction. The interaction changed the secondary and tertiary structures of urease as demonstrated by the circular dichroism study (the decrease in both α- and β-structure percentages). The fluorescence study revealed a change in the tertiary structure. The FTIR for the nanoceria—urease complex showed no changes in the covalent bonds, which indicated the involvement of physical forces in the interaction between urease and nanoceria.