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.
Matsuura
E
E
Department of Cell Chemistry, Institute of Cellular and Molecular Biology, Okayama University Medical School, 2-5-1 Shikata-cho, Okayama 700-8558, Japan.
Inagaki
J
J
Kasahara
H
H
Yamamoto
D
D
Atsumi
T
T
Kobayashi
K
K
Kaihara
K
K
Zhao
D
D
Ichikawa
K
K
Tsutsumi
A
A
Yasuda
T
T
Triplett
D A
DA
Koike
T
T
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