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Binding of dexamethasone by alpha-crystallin
A I Jobling1, A Stevens, R C Augusteyn
1National Vision Research Institute of Australia, 386 Cardigan Street, Carlton, Victoria 3053, Australia.
Investigative Ophthalmology & Visual Science
|June 30, 2001
Summary
Alpha-crystallin, a soluble lens protein, binds dexamethasone, a steroid linked to cataracts. This binding is nonspecific and may explain steroid modification of the protein.
Area of Science:
- Ophthalmology
- Protein Biochemistry
- Pharmacology
Background:
- Long-term steroid use is a risk factor for posterior subcapsular cataract.
- Previous studies indicated soluble lens proteins bind dexamethasone without a specific receptor.
Purpose of the Study:
- To identify the specific soluble protein(s) in the lens responsible for binding glucocorticoids like dexamethasone.
- Investigate the mechanism and characteristics of this binding interaction.
Main Methods:
- Incubation of bovine lens extract with radiolabeled dexamethasone.
- Fractionation of soluble proteins using gel permeation chromatography.
- Binding studies with isolated alpha-crystallin and Scatchard analysis.
- Sequence homology comparisons between lens crystallins and known glucocorticoid-binding proteins.
Main Results:
- Soluble proteins accounted for 52% of total dexamethasone binding in the lens extract.
- Alpha-crystallin was identified as the primary binding protein, responsible for over 98% of soluble binding.
- Dexamethasone binding to alpha-crystallin was characterized as nonspecific partitioning.
- Sequence analysis revealed homology between alpha-crystallins and a yeast corticosteroid-binding protein.
Conclusions:
- Alpha-crystallin is the principal soluble protein in the lens that binds glucocorticoids.
- The binding is nonspecific, likely due to alpha-crystallin's structural properties.
- This nonspecific association may contribute to observed steroid modifications of alpha-crystallin.