@inproceedings{8fee0cdfa25d4e8c8587cdef3310a1a2,
title = "Specific interaction of 7-hydroxyquinoline with Trp-214 in the drug-binding site IIA of human serum albumin",
abstract = "The drug-binding site subdomain IIA of human serum albumin (HSA) was characterized by absorption and fluorescence spectroscopy using 7-hydroxyquinoline (7-HQ) as a local reporter. The spectra of 7-HQ in solution indicate that a ztitterionic tautomer is stabilized by water in the ground state and produces a unique absorption peak at 400 nm and a fluorescence peak at 510 nm. By examining the spectral change in binary mixtures of water and 1,4-dioxane, three water molecules were estimated to stabilize this tautomer through direct interactions with the polar regions of the molecule. When 7-HQ is mixed with HSA, a reduction in the absorbance of the zwitterionic tautomer was observed which indicates a less polar environment around the molecule. The 7-HQ molecule is found to specifically bind in subdomain IIA of HSA and causes a reduction in the fluorescence intensity of the Trp-214 residue which is located in the same binding site. The reduction in the fluorescence of Trp-214 is due to energy transfer from the Trp-214 residue to the 7- HQ probe. The distance between Trp-214 and the probe was calculated using F{\"o}rster theory for energy transfer to be 1.95 nm. This distance and the calculated quenching rate constant using a Stern-Valmer plot (kq = 3.04 x 1012 M-1s-1) both point to a static quenching mechanism. The binding constant and the number of binding sites of the complex were also estimated and the calculations show that the 7-HQ probe binds only in subdomain IIA. The change in the fluorescence intensity of HSA in the presence of the probe indicates that the 7-HQ molecule selectively interacts with the Trp-214 residue which results in partial unmasking of the fluorescence due to the Tyr-263 residue (located in the same site). A much stronger fluorescence from Tyr-263 is observed when HSA is chemically unfolded by 6.0 M GdnHCl. 7- HQ is found to still bind in subdomain IIA in the unfolded state of HSA and causes a reduction in the fluorescence intensities of both Trp-214 and Tyr-263. The present results propose 7-HQ as a useful photophysical probe in studying binding sites in proteins and exploring their hydrophobic environment.",
keywords = "7-Hydroxyquinoline, Biological probes, Chemical unfolding, Drug binding sites, Fluorescence, Human serum albumin, Resonance energy transfer, Tautomerization",
author = "Abou-Zied, {Osama K.} and Najla Al-Lawatia",
year = "2010",
doi = "10.1117/12.840485",
language = "English",
isbn = "9780819479723",
series = "Progress in Biomedical Optics and Imaging - Proceedings of SPIE",
booktitle = "Reporters, Markers, Dyes, Nanoparticles, and Molecular Probes for Biomedical Applications II",
note = "Reporters, Markers, Dyes, Nanoparticles, and Molecular Probes for Biomedical Applications II ; Conference date: 25-01-2010 Through 27-01-2010",
}