Spectroscopic studies of human serum albumin exposed to Fe3O4 magnetic nanoparticles coated with sodium oleate: Secondary and tertiary structure, fibrillation, and important functional properties

Abstract

The structural and functional properties of human serum albumin (HSA) exposed to Fe3O4 magnetic nanoparticles coated with sodium oleate (SOMNPs) were examined by various spectroscopy methods. The results of dynamic light scattering (DLS) indicated the formation of the HSA-SOMNPs complex, referred to as the protein corona. It was found that SOMNPs could quench the intrinsic and synchronous fluorescence of HSA by a static quenching mechanism as evident from time-resolved fluorescence spectroscopy, and could also interfere with the hydrophobic areas of HSA. The values of Ksv, Kb and n were found to be 3.441 × 108 M−1, 7.49 × 108 M−1 and 1.043 at 310 K, respectively. The negative values of ΔH0 (−76.56 kJ mol−1) and ΔS0 (−74.37 J mol−1 K−1) suggested hydrogen bond and Van der Waal's force were the predominant intermolecular forces between the complexes. By following Fluorescence resonance energy transfer (FRET) theory, R0 and r were calculated to be 2.01 nm and 2.26 nm, respectively, which indicated the possibility of energy transfer. Besides, SOMNPs only slightly increased the α-helical content of HSA, and the negative charge of SOMNPs helped to stabilize the secondary structure of HSA. Furthermore, SOMNPs had no significant impact on the formation of HSA fibrillation. The HSA bound to SOMNPs showed higher affinity to copper ions and its drug binding sites Ⅰ and Ⅲ were affected. In addition, SOMNPs also decreased the number of free sulfhydryl groups in HSA and thus reduced its antioxidant property.