title: The binding site in {beta}2-glycoprotein I for ApoER2' on platelets is located in domain V.
abstract: The antiphospholipid syndrome is caused by autoantibodies directed against beta(2)-glycoprotein I (beta(2)GPI). Dimerization of beta(2)GPI results in an increased platelet deposition to collagen. We found that apolipoprotein E receptor 2' (apoER2'), a member of the low density lipoprotein receptor family, is involved in activation of platelets by dimeric beta(2)GPI. To identify which domain of dimeric beta(2)GPI interacts with apoER2', we have constructed domain deletion mutants of dimeric beta(2)GPI, lacking domain I (DeltaI), II (DeltaII), or V (DeltaV), and a mutant with a W316S substitution in the phospholipid (PL)-insertion loop of domain V. DeltaI and DeltaII prolonged the clotting time, as did full-length dimeric beta(2)GPI; DeltaV had no effect on the clotting time. Second, DeltaI and DeltaII bound to anionic PL, comparable with full-length dimeric beta(2)GPI. DeltaV and the W316S mutant bound with decreased affinity to anionic PL. Platelet adhesion to collagen increased significantly when full-length dimeric beta(2)GPI, DeltaI, or DeltaII (mean increase 150%) were added to whole blood. No increase was found with plasma beta(2)GPI, DeltaV, or the W316S mutant. Immunoprecipitation indicated that full-length dimeric beta(2)GPI, DeltaI, DeltaII, and the W316S mutant can interact with apoER2' on platelets. DeltaV did not associate with apoER2'. We conclude that domain V is involved in both binding beta(2)GPI to anionic PL and in interaction with apoER2' and subsequent activation of platelets. The binding site in beta(2)GPI for interaction with apoER2' does not overlap with the hydrophobic insertion loop in domain V.
authors.affiliation: Department of Haematology and Rheumatology, University Medical Center, 3508GA Utrecht, The Netherlands.
authors.forename: Menno
authors.initials: M
authors.lastname: van Lummel
authors.forename: Maarten T T
authors.initials: MT
authors.lastname: Pennings
authors.forename: Ronald H W M
authors.initials: RH
authors.lastname: Derksen
authors.forename: Rolf T
authors.initials: RT
authors.lastname: Urbanus
authors.forename: Bianca C H
authors.initials: BC
authors.lastname: Lutters
authors.forename: Niels
authors.initials: N
authors.lastname: Kaldenhoven
authors.forename: Philip G
authors.initials: PG
authors.lastname: de Groot
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D001665:Binding Sites; D001777:Blood Coagulation; D001792:Blood Platelets / Q000378:metabolism*; D002478:Cells, Cultured; D003094:Collagen / Q000378:metabolism; D006224:Cricetinae; D019281:Dimerization; D006023:Glycoproteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D006801:Humans; D047468:Immunoprecipitation; D007668:Kidney / Q000166:cytology / Q000378:metabolism; D026502:LDL-Receptor Related Proteins; D008533:Megakaryocytes / Q000166:cytology / Q000378:metabolism; D010446:Peptide Fragments / Q000494:pharmacology; D010743:Phospholipids / Q000378:metabolism*; D010957:Plasmids; D015539:Platelet Activation; D017434:Protein Structure, Tertiary; D018110:Receptors, Lipoprotein / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D017384:Sequence Deletion; D014470:Umbilical Cord / Q000166:cytology / Q000378:metabolism; D053482:beta 2-Glycoprotein I
chemical_list: D006023:Glycoproteins; D026502:LDL-Receptor Related Proteins; D010446:Peptide Fragments; D010743:Phospholipids; D018110:Receptors, Lipoprotein; D053482:beta 2-Glycoprotein I; C098773:low density lipoprotein receptor-related protein 8; D003094:Collagen