Specific interaction of 7-hydroxyquinoline with Trp-214 in the drug-binding site IIA of human serum albumin

Osama K. Abou-Zied, Najla Al-Lawatia

Research output: Chapter in Book/Report/Conference proceedingConference contribution

1 Citation (Scopus)

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 Förster 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.

Original languageEnglish
Title of host publicationProgress in Biomedical Optics and Imaging - Proceedings of SPIE
Volume7576
DOIs
Publication statusPublished - 2010
EventReporters, Markers, Dyes, Nanoparticles, and Molecular Probes for Biomedical Applications II - San Francisco, CA, United States
Duration: Jan 25 2010Jan 27 2010

Other

OtherReporters, Markers, Dyes, Nanoparticles, and Molecular Probes for Biomedical Applications II
CountryUnited States
CitySan Francisco, CA
Period1/25/101/27/10

Keywords

  • 7-Hydroxyquinoline
  • Biological probes
  • Chemical unfolding
  • Drug binding sites
  • Fluorescence
  • Human serum albumin
  • Resonance energy transfer
  • Tautomerization

ASJC Scopus subject areas

  • Biomaterials
  • Electronic, Optical and Magnetic Materials
  • Radiology Nuclear Medicine and imaging
  • Atomic and Molecular Physics, and Optics

Fingerprint Dive into the research topics of 'Specific interaction of 7-hydroxyquinoline with Trp-214 in the drug-binding site IIA of human serum albumin'. Together they form a unique fingerprint.

Cite this