Study on the impacts of Co2+ on the tobacco etch virus protease

Tobacco etch virus protease (TEVp) is an important enzyme with unique and highly-conserved enzymatic activity. Co 2+ has special biological toxicity. In order to understand the influence of Co 2+ on the structure of TEVp, we determined the intrinsic fluorescence emission and synchronous fluorescence spectroscopies reflecting the regulation of TEVp structure by Co 2 . The fluorescence emission and the synchronous fluorescence spectra suggested that Co 2+ quenched the fluorescence of TEVp significantly and led to the increase in the hydrophobicity of tryptophan and tyrosine residues. Under the conditions of 300 K and 311 K, the quenching constant K sv was found to be 4.161×10 2 L/mol and 2.129×10 2 L/mol, respectively; the binding constant K A was 6.625×10 3 L/mol and 5.132×10 3 L/mol, respectively. Moreover, the dynamic fluorescence quenching rate constant K q was much greater than the maximum value of the diffusion collision quenching rate constant, 2.0×10 10 L mol -1 s -1 , suggesting the quenching mechanism was static quenching. The Gibbs free energy ΔG < 0, the enthalpy value ΔH < 0 and the entropy value ΔS > 0, indicated the spontaneous interaction between Co 2+ and TEVp, and that electrostatic force played a major role when Co 2+ binds to TEVp. Our studies analyzed the influences of Co 2+ on various fluorescence spectra of TEVp and revealed the mechanism of the impacts of Co 2+ on the structure of TEVp, thus laying the ground for the efficient utilization of TEVp in the fields of biology and biological