The secondary and aggregation structural changes of BSA induced by trivalent chromium: A biophysical study

Trivalent chromium Cr(III), which was originally considered to be innocuous as a nutriment, has been suspected to induce some abnormalities in human body recently. In the present work, the effects of Cr(III) on the structural state of BSA were comprehensively investigated through a series of appropriate methods in combination, including X-ray photoelectron spectroscopy (XPS), fourier transform infrared spectroscopy (FTIR), circular dichroism (CD), UV-vis absorption, synchronous fluorescence, fluorescence lifetime analysis, resonance light scattering (RLS), dynamic light scattering (DLS) and excitation-emission matrix spectroscopy (EEMS) methods. XPS accurately described the binding activity of Cr(III) with protein C, N and O atoms. The structural analysis according to FTIR and CD methods showed that the Cr(III) binding altered BSA conformation with a major reduction of α-helix. RLS and DLS analyses demonstrated that the presence of Cr(III) with low concentration could induce the aggregation structural changes of BSA. UV-vis absorption, EEMS and synchronous fluorescence suggested that the interaction between Cr(III) and BSA induced a slight unfolding of the polypeptide backbone and altered the microenvironments of Trp and Tyr residues in BSA. This research is helpful for understanding the structure-function relationship involved in metal ion-protein bioconjugate process.