Uttam Pal - Interaction of Merocyanine 540 with serum albumins: photophysical and binding studies

Document created by Uttam Pal on Dec 25, 2015
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  Banerjee, Mousumi, Pal, Uttam, Subudhhi, Arijita, Chakrabarti,   Abhijit, Basu, Samita 108 23-33

  Abstract: Photophysical studies on binding   interactions of a negatively charged anti-tumor photosensitizer,   Merocyanine 540 (MC 540), with serum proteins, bovine serum   albumin (BSA) and human serum albumin (HSA), have been performed   using absorption and steady-state as well as time-resolved   fluorescence techniques. Formation of ground state complex has   been confirmed from the detailed studies of absorption spectra of   MC 540 in presence of SAs producing isosbestic points. Binding   between the proteins and MC 540, which perturbs the existing   equilibrium between the fluorescent monomer and its   non-fluorescent dimer, induces a remarkable enhancement in   fluorescence anisotropy and intensity of MC 540 along with a red   shift of its maximum. The binding stoichiometry of MC 540 and SAs   are more than 1.0 which depicts that two types of complexes,   i.e., 1:1 and 2:1 are formed with addition of varied   concentration of protein. Both the steady-state and time-resolved   fluorescence results show that in 2:1 complex one of the MC 540   molecules is exposed towards aqueous environment with a greater   extent when bound with HSA compared to BSA due to the structural   flexibility of that protein. Thermodynamic analyses using van't   Hoff plot indicate that the binding between MC 540 and individual   SA is an entropy-driven phenomenon. The probable hydrophobic   binding site has been located by denaturation of proteins,   micropolarity measurement and Förster resonance energy transfer   and that is further supported by molecular docking studies.   Changes in circular dichroism spectra of BSA in presence of MC   540 depict secondary structural changes of the protein. The   induced-CD shows that BSA due to its rigid structure generates   chirality in MC 540 much more efficiently compared to HSA.

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