Protein conformation changes induced by a novel organophosphate-containing water-soluble derivative of a C60 fullerene nanoparticle

Water-soluble fullerene derivatives have attracted great attention in biological and medical applications. In particular, for any potential in vivo application, the interaction of water-soluble fullerene nanoparticles with human serum albumin (HSA) is crucial. In this study, we synthesized a novel organophosphate-containing water-soluble derivative of C-60 (C60Om(OH)(n)(C(PO3Et2)(2))(l) (m approximate to 8, n approximate to 12, and l approximate to 1), abbreviated as TEMDP-CF). To explore the influence of an organophosphate-containing water-soluble derivative Of C60 nanoparticles on the conformational changes of HSA, we have investigated the interaction of TEMDP-CF with HSA by biophysical methods, mainly P-31 NMR, MALDI-TOF mass spectroscopy, fluorescence, fluorescence dynamics, UV spectroscopy, FT-IR, and CD, for the first time. 31 P NMR and MALDI-TOF MS analysis have proven the formation of the HSA-TEMDP-CF complex, which is further confirmed by fluorescence and fluorescence dynamics results. We observed a quenching of fluorescence of HSA in the presence of TEMDP-CF and also analyzed the quenching results using the modified Stern-Volmer equation, and a red shift in the emission maximum wavelength can be explained as the result of changes in the ternary structure near the binding site. From fluorescence, fluorescence dynamics, and energy transfer experiment parameters, we can predict the possible binding position of TEMDP-CF on the HSA at the site of subdomain IIA, which also agrees with the reported literature. Most significantly, the percentage of the HSA alpha-helix and beta-sheet structure increased, and the beta-turn structure decreased in the CD and FTIR analysis results, revealing that the protein becomes more compact upon association with TEMDP-CF. Furthermore, the increase of the alpha-helix amount, at least on the structure of HSA, may ascribe to the distinct property of the water-soluble TEMDP-CF nanoparticles.