Ms. Najla Murtadha Al-Lawatia Profile

Najla Murtadha Al-Lawatia

at Sultan Qaboos Univ

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Publications (2)

Proceedings Article | 2 February 2012 Paper

Water participation in molecular recognition and protein-ligand association: Probing the drug binding site "Sudlow I" in human serum albumin

Najla Al-Lawatia, Thomas Steinbrecher, Osama Abou-Zied

Proceedings Volume 8233, 82331D (2012) https://doi.org/10.1117/12.905809

KEYWORDS: Luminescence, Molecules, Proteins, Molecular interactions, Absorption, Molecular spectroscopy, Hydrogen, Spectroscopy, Energy transfer, Blood

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Proceedings Article | 17 February 2010 Paper

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

Proceedings Volume 7576, 757618 (2010) https://doi.org/10.1117/12.840485

KEYWORDS: Luminescence, Molecules, Absorption, Proteins, Molecular interactions, Energy transfer, Binary data, Absorbance, Solids, Resonance energy transfer

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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 (k_q = 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.

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