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Epitopes on beta2-GPI recognized by anticardiolipin antibodies
T Koike1, K Ichikawa, H Kasahara
1Department of Medicine II, Hokkaido University School of Medicine, Sapporo, Japan. tkoike@med.hokudai.ac.jp
Lupus
|November 14, 1998
Summary
Anticardiolipin antibodies (aCL) target a hidden site on beta2-glycoprotein I (beta2-GPI) when it binds to membranes. Researchers identified this cryptic epitope on domain IV of beta2-GPI using advanced modeling and biopanning techniques.
Area of Science:
- Immunology
- Structural Biology
- Biochemistry
Background:
- Anticardiolipin antibodies (aCL) are key biomarkers in antiphospholipid syndrome (APS).
- These antibodies recognize specific epitopes on beta2-glycoprotein I (beta2-GPI).
- The epitope is typically cryptic, becoming accessible only upon beta2-GPI interaction with negatively charged phospholipids or surfaces.
Purpose of the Study:
- To elucidate the structural basis of aCL recognition of beta2-GPI.
- To identify the specific domain and sequence of beta2-GPI targeted by aCL.
- To model the three-dimensional structure of beta2-GPI.
Main Methods:
- Homology modeling of beta2-GPI using NMR data of sushi domains.
- Construction of a five-domain cylindrical model of beta2-GPI.
- Phage-displayed random peptide library biopanning to identify aCL epitopes.
Main Results:
- The beta2-GPI model revealed a cylindrical structure with domains IV and V interacting electrostatically.
- Biopanning identified consensus peptide sequences that mimic the aCL epitope.
- These sequences showed structural similarity to a region within domain IV of beta2-GPI.
Conclusions:
- The cryptic epitope recognized by aCL is located on domain IV of beta2-GPI.
- Electrostatic interactions play a role in the conformation and epitope exposure of beta2-GPI.
- This structural understanding aids in diagnosing and potentially treating antiphospholipid syndrome.