Investigation on the molecular interaction between dietary flavone luteolin and alpha-2-macroglobulin using multi-spectroscopic, calorimetric and molecular dynamics simulation techniques

The current study examined the mechanism of interaction between luteolin and human αlpha-2-macroglobulin (α2M) to determine the binding mode and the interaction of the ligand using biophysical and molecular modelling methods. The UV-absorbance confirmed the formation of a complex between α2M and luteolin. Luteolin considerably reduced the intrinsic fluorescence of α2M via dynamic quenching determined by fluorescence quenching. The binding process was spontaneous and moderate (Kb = 0.70 × 104 M−1, 300 K), and the hydrophobic interaction was a significant factor in their interaction. With increasing luteolin concentration, the anti-proteolytic activity of α2M declines by approximately 35 % of its native functional activity. Förster energy was used to determine the energy transfer and the binding distance between the ligand and the protein which was found to be 2.77 nm for the α2M-luteolin complex in accordance with fluorescence resonance energy transfer (FRET). Synchronous fluorescence and red-edge excitation shift (REES) data were used to determine the changes in the microenvironment around Tyr and Trp residues in the presence of luteolin. The circular dichroism (CD) showed changes in conformation upon binding of luteolin to α2M. The Fourier transform infrared spectroscopy (FTIR) spectra provided additional evidence that the secondary structure of α2M was considerably altered by the addition of luteolin. The molecular docking simulation revealed that, in addition to hydrophobic interactions, the hydrogen bonds were involved in the interaction of α2M-luteolin complex.