Influence of structure of human, rat, and bovine serum albumins on binding properties of photoactive drug hypericin

Fluorescence binding measurements and molecular modeling were employed to study the interaction of hypericin (Hyp) with human (HSA), rat (RSA), and bovine (BSA) serum albumins. Fluorescence emission data show the solubility of Hyp increasing in the order BSA, HSA, and RSA. Molecular modeling was used to construct the detailed structural models of the complexes and to explain the differences in the binding properties of Hyp. It was shown that the structures of Hyp/HSA and Hyp/RSA complexes are more similar and in some aspects different from those found for the Hyp/BSA complex. The role of the amino acid sequence in the IIA subdomains of HSA, RSA, and BSA is discussed to explain the observed differences.