Abstract

The study of binding mechanisms and any associated conformational changes of human serum transferrin (Tf) on interaction with cyanine dye 3,3'-di(3-sulfopropy1)-4,5,4',5'-dibenzo-9-methyl-thiacarbocyanine triethylam-monium salt (MTC) are of great importance in the process of Tf targeting dye delivery into cancer cells. It is possible to lay theoretical foundations for cyanine dye as a potential photosensitizer to achieve the photodynamic therapy (PDT). The mechanisms of interaction between MTC and Tf were portrayed by means of fluorescence spectra, UV-vis absorption spectra, synchronous fluorescence spectra, circular dichroism (CD) and molecular dynamic docking. The data of fluorescence spectra displayed that the formation of MTC-Tf complex is a static quenching process through van der Waals forces and hydrogen bonds with a high affinity of 10(9) M-1. Binding distance between MTC and Tf substantiated that the non-radioactive energy transfer mechanism is also involved in the fluorescence quenching of protein. Furthermore, structural analysis indicated that MTC binding result in an increased of ce.-helix content and an increased hydrophobic around the tryptophan residues of Tf as well as a certain structural changes in Tf, which confirmed by the CD, synchronous fluorescence and UV-vis experiments. Additionally, the results of molecular dynamic docking elucidated that the dye was located in N-lobe of Tf. (C) 2015 Elsevier B.V. All rights reserved.

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