Proteolytic cleavage of beta(2)-glycoprotein I: reduction of antigenicity and the structural relationship.
Binding of beta(2)-glycoprotein I (beta(2)-GPI)-dependent anticardiolipin antibodies (aCL) derived from antiphospholipid syndrome (APS) is significantly reduced in aCL ELISA due to loss of the phospholipid (PL) binding property of beta(2)-GPI by plasmin treatment. In the present study, the treatment generated a nicked form of beta(2)-GPI and resulted in loss of antigenicity for the autoantibodies detected in ELISA, using an beta(2)-GPI directly adsorbed polyoxygenated carboxylated plate, the assay system of which was not related to PL binding. The nicked form bound to neither Cu(2+)-oxidized low-density lipoprotein (oxLDL) nor to beta(2)-GPI-specific lipid ligands isolated from oxLDL, the result being a complete loss of subsequent binding of anti-beta(2)-GPI autoantibodies. The conformational change in the nicked domain V was predicted from its intact structure determined by an X-ray analysis (implemented in Protein Data Bank: 1C1Z), molecular modeling and epitope mapping of a monoclonal anti-beta(2)-GPI antibody, i.e. Cof-18, which recognizes the related structure. The analysis revealed that novel hydrophobic and electrostatic interactions appeared in domain V after the cleavage, thereby affecting the PL binding of beta(2)-GPI. Such a conformational change may have important implications for exposure of cryptic epitopes located in the domains such as domain IV.
Department of Cell Chemistry, Institute of Cellular and Molecular Biology, Okayama University Medical School, 2-5-1 Shikata-cho, Okayama 700-8558, Japan.
E
E
Matsuura
J
J
Inagaki
H
H
Kasahara
D
D
Yamamoto
T
T
Atsumi
K
K
Kobayashi
K
K
Kaihara
D
D
Zhao
K
K
Ichikawa
A
A
Tsutsumi
T
T
Yasuda
D A
DA
Triplett
T
T
Koike
D000595:Amino Acid Sequence; D017153:Antibodies, Anticardiolipin / Q000378:metabolism; D000911:Antibodies, Monoclonal / Q000276:immunology; D000937:Antigen-Antibody Reactions / Q000187:drug effects; D001667:Binding, Competitive; D016384:Consensus Sequence; D003300:Copper / Q000494:pharmacology; D004797:Enzyme-Linked Immunosorbent Assay; D000939:Epitopes / Q000737:chemistry / Q000276:immunology; D005341:Fibrinolysin / Q000378:metabolism* / Q000494:pharmacology; D006023:Glycoproteins / Q000737:chemistry* / Q000276:immunology / Q000378:metabolism; D006801:Humans; D008024:Ligands; D008077:Lipoproteins, LDL / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding / Q000187:drug effects; D011487:Protein Conformation / Q000187:drug effects; D017434:Protein Structure, Tertiary; D013329:Structure-Activity Relationship; D013379:Substrate Specificity; D053482:beta 2-Glycoprotein I
D017153:Antibodies, Anticardiolipin; D000911:Antibodies, Monoclonal; D000939:Epitopes; D006023:Glycoproteins; D008024:Ligands; D008077:Lipoproteins, LDL; D053482:beta 2-Glycoprotein I; C099252:oxidized low density lipoprotein; D003300:Copper; D005341:Fibrinolysin