Interaction of curcumin with intravenous immunoglobulin: A fluorescence quenching and Fourier transformation infrared spectroscopy study

The interaction of curcumin with intravenous immunoglobulin (IVIG) mainly composed of immune gamma globulin (IgG) was studied in vitro by spectroscopic methods including fluorescence spectroscopy and Fourier transformation infrared (FTIR) spectroscopy. Docking was used to calculate the interaction mode between curcumin and IVIG. The binding parameters for the reaction were calculated according to the Sips equation, which suggested that the binding of IVIG to curcumin was characterized by two binding sites with the average affinity constant Ko at 1.170×104 M−1 (296 K), and it was a non-specific and weak drug–protein interaction. The secondary structure compositions of free IVIG and its curcumin complexes were calculated by the FTIR difference spectra, self-deconvolution, second derivative resolution enhancement and the curve-fitting procedures of amide I band. The observed spectral changes indicate a partial unfolding of the protein structure, but the typical β structural conformation of IVIG is still retained. The average binding distance between curcumin and the chromophore of IVIG (5.57 nm) was obtained using the theory of Förster energy transfer. IVIG can serve as transport protein (carrier) for curcumin.