Abstract:

PEG200-niclosamide was obtained from niclosamide. The interaction between keyhole limpet hemocyanin(KLH) and niclosamide/PEG200-niclosamide was investigated by fluorescence spectra, synchronous fluorescence spectra, ultraviolet absorption spectra and circular dichroism(CD) spectra. It was shown that KLH fluorescence at 340 nm was quenched regularly with the addition of niclosamide/PEG200-niclosamide; the quenching constant decreased as temperature increased; and the quenching mechanism with KLH was suggested as a static fluorescence quenching process. The binding constants(K) were obtained respectively according to Lineweaver-Burk equation at different temperatures, while there was a weaker interaction of the PEG200-niclosamide with KLH than that with niclosamide. The calculated thermodynamic parameters(ΔH, ΔS) by Van′t Hoff equation indicated that the electrostatic interaction played major roles in the binding processes. The binding processes of KLH with niclosamide/PEG200-niclosamide were spontaneous inter-molecular interaction in which entropy increased and Gibbs free energy decreased. The distances between KLH and niclosamide/PEG200-niclosamide were less than 7 nm according to the theory of the Frster energy transference. The effects of niclosamide and PEG200-niclosamide on the conformation of KLH were further analyzed by synchronous fluorescence spectra and circular dichroism spectra. Both niclosamide and PEG200-niclosamide could be deposited and transported by KLH and they affected the conformation of KLH. The CD spectra proved that the α-helix contents of KLH decreased, and the relative contents of secondary structure units of KLH changed in these binding processes. The relationship between the molecule structures and their binding ability was discussed preliminarily by comparison of the interactions between KLH and niclosamide/PEG200-niclosamide..

Key words: Keyhole limpet hemocyanin; Ultraviolet spectroscopy; Fluorescence spectroscopy; Synchronous fluorescence spectroscopy; Circular dichroism spectrometry