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Different forms of the oxysterol-binding protein. Binding kinetics and stability
The Journal of Biological Chemistry
|October 25, 1984
Summary
The oxysterol-binding protein exists in three forms, with its structure and stability changing upon sterol binding and pH shifts. Ligand binding stabilizes the protein, while acidic conditions or time can cause dissociation.
Area of Science:
- Biochemistry
- Molecular Biology
- Protein Structure
Background:
- Oxysterol-binding proteins (OSBP) are crucial for lipid transport and homeostasis.
- Understanding OSBP conformational changes is key to elucidating its biological functions.
Purpose of the Study:
- To characterize the different forms of oxysterol-binding protein.
- To investigate the effects of sterol binding and environmental conditions on OSBP structure and stability.
Main Methods:
- Sedimentation coefficient and Stokes radius measurements.
- Sucrose gradient ultracentrifugation.
- Protein purification and activity assays.
Main Results:
- Three distinct forms of oxysterol-binding protein were identified based on size, symmetry, and subunit composition.
- Ligand binding (25-hydroxycholesterol) reduced protein size and increased symmetry by dissociating a subunit.
- Protein dissociation was induced by low pH or prolonged incubation, with the liganded form showing greater stability.
Conclusions:
- Oxysterol-binding protein undergoes significant structural rearrangements upon sterol binding.
- Environmental factors like pH and urea influence OSBP quaternary structure and stability.
- The liganded form of OSBP exhibits enhanced stability compared to the unliganded form.