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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 (h-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 h-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 h-Mb at pH 7.4 revealed that the Au/ZnO NCs decrease the thermodynamic stability of h-Mb. Investigation of Au/ZnO NC's effects on urea concentration-dependent unfolding free energy of h-Mb at pH 7.4 showed that the Au/ZnO NCs strengthen the urea impact to decrease the thermodynamic stability of h-Mb. The quantitative estimation of enthalpic and entropic contributions to the Au/ZnO NCs-mediated decrease in the unfolding free energy of h-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 h-Mb with Au/ZnO NCs. ITC and time-resolved fluorescence studies of h-Mb further suggest that the Au/ZnO NCs form binding interactions with h-Mb at pH 7.4.
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