Electrochemical and spectroscopic studies on the conformational structure of hemoglobin assembled on gold nanoparticles.

Protein conformational changes may be associated with particular properties such as function, transportation, assembly, tendency to aggregate, and potential cytotoxicity. Protein misfolding, in particular, has been intimately related to protein-mediated diseases. In this study, the conformational structure changes of hemoglobin (Hb) induced by the assembly on gold nanoparticles (AuNPs) surface were studied in detail by a combination of electrochemical method and various spectroscopic techniques including UV-vis absorption, fluorescence, circular dichroism (CD), and Fourier transform infrared (FTIR) spectroscopy. The results indicated that Hb in the Hb-AuNPs bioconjugate system that was prepared by the assembly of Hb on the surface of AuNPs underwent substantial conformational changes both at secondary and tertiary structure level. The assembly of Hb on the boundary surface of AuNPs could result a disturbance of the structure of Hb and induce the exposure of the heme group and tryptophan (Trp) residues to the solvent, leading to the enhancement in the electron transfer rate of the protein. The calculation from quantitative second-derivative infrared and CD spectra of the Hb-AuNPs bioconjugate system showed that AuNPs could induce the conversion of alpha-helix to beta-sheet structures and unfolding of the protein. Moreover, the effects of the concentration and the size of AuNPs on the conformational structure changes of Hb in the bioconjugate system were also demonstrated. The results obtained here not only provide the detailed conformational behavior of Hb molecules on nanoparticles, but also create a framework for analyzing the biosafety of nanoparticles in terms of the biological behavior of biomacromolecules.