Deciphering the Underlying Mechanism for Au/ZnO Nanocomposites-Induced Modulation of Structural Features and Thermodynamic Stability of Horse Myoglobin

Au/ZnO nanocomposites (NCs) were synthesized and characterized by using various analytical techniques. Analysis of Au/ZnO NCs effect on ¹H NMR, CD, fluorescence, and absorbance spectra of horse myoglobin (<i>h</i>-Mb) at 0.0 and 5.0 M urea (pH 7.4) revealed that the Au/ZnO NCs weaken the heme-globin interactions and also disrupt the secondary/tertiary structure of <i>h</i>-Mb. Furthermore, the Au/ZnO NCs effect of weakening the heme-globin interactions and disrupting the protein structures was detected more in the denaturant media than in the aqueous solution. Analysis of the Au/ZnO NCs effect on thermodynamic parameters (based on absorbance at 409 nm, CD at 222 nm, and DSC) of <i>h</i>-Mb at pH 7.4 revealed that the Au/ZnO NCs decrease the thermodynamic stability of <i>h</i>-Mb. Investigation of Au/ZnO NC's effects on urea concentration-dependent unfolding free energy of <i>h</i>-Mb at pH 7.4 showed that the Au/ZnO NCs strengthen the urea impact to decrease the thermodynamic stability of <i>h</i>-Mb. The quantitative estimation of enthalpic and entropic contributions to the Au/ZnO NCs-mediated decrease in the unfolding free energy of <i>h</i>-Mb reveals that the Au/ZnO NCs decrease the local (heme-globin interactions) and structural thermodynamic stability of the protein due to the enthalpic interactions of <i>h</i>-Mb with Au/ZnO NCs. ITC and time-resolved fluorescence studies of <i>h</i>-Mb further suggest that the Au/ZnO NCs form binding interactions with <i>h</i>-Mb at pH 7.4.