Interaction of antiviral and antitumor photoactive drug hypocrellin A withhuman serum albumin

Absorption, resonance Raman, surface-enhanced Raman spectroscopy and differ ential scanning microcalorimetry were employed to study the interaction of hypocrellin A with human serum albumin. The identification of the binding p lace for hypocrellin A as well as the model for the albumin-hypocrellin A c omplex are proposed. In this model hypocrellin A interacts with albumin thr ough more than one binding site placed on the protein surface. This model o f non-specific interaction could explain why the absorption spectrum of hyp ocrellin A does not change in the presence of albumin and why the presence of the drug does not change significantly the thermodynamic parameters of t he protein, while the Raman spectra show evident changes concerning both th e protein and the drug structure. Even if hypocrellin A does not interact w ith an interior binding site, it can affect deeply the general albumin stru cture.