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Structural changes in human tear lipocalins associated with lipid binding
O K Gasymov1, A R Abduragimov, T N Yusifov
1Departments of Pathology and Ophthalmology, UCLA School of Medicine, 100 Stein Plaza, Los Angeles, CA 90095, USA.
Biochimica Et Biophysica Acta
|July 24, 1998
Summary
Tear lipocalins (TL) undergo structural changes upon ligand binding and release. Acidic conditions trigger lipid release via a molten globule state, suggesting a mechanism for tear film lipid delivery.
Area of Science:
- Biochemistry
- Structural Biology
- Ophthalmology
Background:
- Tear lipocalins (TL) are proteins found in the tear film.
- Their role in lipid binding and delivery is crucial for ocular surface health.
- Understanding their conformational dynamics is key to their function.
Purpose of the Study:
- To investigate the structural and conformational changes in tear lipocalins.
- To elucidate the mechanism of ligand binding and release, particularly lipids.
- To explore the role of pH in TL conformational dynamics and lipid liberation.
Main Methods:
- Circular dichroism (CD) spectroscopy to assess secondary structure and rigidity.
- Analysis of aromatic amino acid exposure (tyrosine, tryptophan).
- Electron paramagnetic resonance (EPR) studies to monitor lipid release under varying pH conditions.
Main Results:
- Ligand binding induces beta-sheet formation and increased rigidity in TL.
- Acidic pH triggers conformational changes, exposing aromatic residues and leading to lipid release.
- Lipid liberation from TL occurs via a molten globule state at acidic pH.
Conclusions:
- Tear lipocalins undergo significant conformational changes in response to ligand binding and pH.
- Acidic environments, such as those at lipid-aqueous interfaces, promote lipid release from TL.
- These findings suggest a regulatory mechanism for lipid delivery by TL at the tear film surface.