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Solubilization of the functional C5a receptor from human polymorphonuclear leukocytes
T E Rollins1, S Siciliano, M S Springer
1Department of Immunology Research, Merck Sharp and Dohme Research Laboratories, Rahway, New Jersey 07065.
The Journal of Biological Chemistry
|January 5, 1988
Summary
Researchers extracted the active C5a receptor from human immune cells. This soluble receptor exists in two forms, with binding C5a potentially converting a smaller form to a larger, oligomeric structure.
Area of Science:
- Immunology
- Molecular Biology
- Biochemistry
Background:
- The C5a receptor (C5aR) plays a crucial role in inflammatory responses.
- Understanding the structural dynamics of C5aR is key to modulating immune cell activation.
Purpose of the Study:
- To characterize the biophysical properties of the C5a receptor in a solubilized, active state.
- To investigate the oligomeric state and ligand-induced conformational changes of the C5a receptor.
Main Methods:
- Solubilization of C5a receptor from human polymorphonuclear leukocytes using detergents.
- Gel filtration chromatography to determine molecular mass and oligomeric state.
- Cross-linking studies to identify receptor complexes.
Main Results:
- The solubilized C5a receptor retains high-affinity C5a binding (Kd = 90 pM).
- The receptor exists in two forms: a smaller (30-70 kDa) nonliganded form and a larger (150-200 kDa) form, likely oligomeric.
- C5a binding promotes conversion to the larger form, suggesting oligomerization upon ligand engagement.
- Cross-linking revealed complexes of 52 kDa (C5a-binding subunit adduct) and 95 kDa (adduct with additional polypeptide).
Conclusions:
- The C5a receptor exists in distinct conformational states, with ligand binding inducing oligomerization.
- These findings provide insights into the structural basis of C5a receptor function and signaling.
- The characterized receptor forms and complexes offer targets for therapeutic intervention in inflammatory diseases.