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 language | English |
|---|---|
| Title of host publication | Progress in Biomedical Optics and Imaging - Proceedings of SPIE |
| Volume | 7576 |
| DOIs | |
| Publication status | Published - 2010 |
| Event | Reporters, Markers, Dyes, Nanoparticles, and Molecular Probes for Biomedical Applications II - San Francisco, CA, United States Duration: Jan 25 2010 → Jan 27 2010 |
Other
| Other | Reporters, Markers, Dyes, Nanoparticles, and Molecular Probes for Biomedical Applications II |
|---|---|
| Country | United States |
| City | San Francisco, CA |
| Period | 1/25/10 → 1/27/10 |
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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
Cite this
Specific interaction of 7-hydroxyquinoline with Trp-214 in the drug-binding site IIA of human serum albumin. / Abou-Zied, Osama K.; Al-Lawatia, Najla.
Progress in Biomedical Optics and Imaging - Proceedings of SPIE. Vol. 7576 2010. 757618.Research output: Chapter in Book/Report/Conference proceeding › Conference contribution
}
TY - GEN
T1 - Specific interaction of 7-hydroxyquinoline with Trp-214 in the drug-binding site IIA of human serum albumin
AU - Abou-Zied, Osama K.
AU - Al-Lawatia, Najla
PY - 2010
Y1 - 2010
N2 - 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.
AB - 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.
KW - 7-Hydroxyquinoline
KW - Biological probes
KW - Chemical unfolding
KW - Drug binding sites
KW - Fluorescence
KW - Human serum albumin
KW - Resonance energy transfer
KW - Tautomerization
UR - http://www.scopus.com/inward/record.url?scp=77951794870&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=77951794870&partnerID=8YFLogxK
U2 - 10.1117/12.840485
DO - 10.1117/12.840485
M3 - Conference contribution
SN - 9780819479723
VL - 7576
BT - Progress in Biomedical Optics and Imaging - Proceedings of SPIE
ER -