In this study, the catalase-like activity of monomeric tau protein was reported in the presence of of zinc (Zn(II)) ions at low pH value. Monomeric tau protein contains two SH groups that are a target of disulfide bond formation. However these SH groups are able to interact with Zn(II) ion at pH 7.2 which creates a thiol bond as a mimetic model of chloroperoxidase active site which performs catalase like activity at low pH. Zn(II)/tau protein complex decomposed H2O2 with a high rate (Vm) as well as an efficient turn oven number (kcat) at pH 3. This remarkable catalase like activity is may be attributed to the conformational reorientation of protein at low pH. Circular dichroism (CD) studies did not demonstrate any secondary structural changes of tau protein after addition of Zn(II) ions at pH 7.2. In addition, tau protein shows identical CD bands at pH 7.2 and 3. Moreover, fluorescence quenching of tau by Zn(II) at pH 7.2 was initiated by complex formation rather than by dynamic collision. A significant red shift (6nm) was observed in the emission maximum of the fluorescence spectra when the protein was dissolved at pH 3 compared to pH 7.2. This conformational change can provide information regarding the rearrangements of the protein structure and exposure of Cys-Zn(II) group to the solvent which induces easy access of active site to H2O2 molecules and corresponding enhanced catalytic activity of Zn(II)/tau protein complex. This study introduces tau protein as a bio-inspired high performing scaffold for transition metal encapsulation and introducing an engineered apoprotein-induced biomimetic enzyme.
Herein we have engineered a micellar Cu protoporphyrin catalyst that mediates carbon bond activation using peroxide as an electron source. Cu protoporphyrin is a biomimetic model of active site of chloroperoxidase enzyme, which catalyzes the carbon bond halogenation in the presence of a suitable amount of H2O2. The encapsulation of Cu(II) Protoporphyrin IX/L-Cysteine inside of cetyltrimethylammonium bromide micelle increases the rate of chlorination at pH 3. The cited catalyst resists high concentrations of hydrogen peroxide, which is previously reported as a suicide inactivator component of hemo-enzymes. Isothermal Titration Calorimetry (ITC) and Dynamic Light Scattering (DLS) data have revealed the formation of a micellar complex by encapsulation of six Cu(II) proporphyrins within each micelle. Moreover, electrochemical investigations indicate that L-Cysteine increases the intensity of electron transferred due to the formation of self-assembled monolayer on Au electrode. Our results paved a road toward the design of a more robust mimetic catalysis based on Protoporphyrin IX derivatives.