title: Evolutionary conservation of the lipopolysaccharide binding site of β₂-glycoprotein I.
abstract: β₂-Glycoprotein I (β₂GPI) is a highly abundant plasma protein and the major antigen for autoantibodies in the antiphospholipid syndrome. Recently, we have described a novel function of β₂GPI as scavenger of lipopolysaccharide (LPS). With this in mind we investigated the conservation of β₂GPI in vertebrates and set out to identify the binding site of LPS within β₂GPI. The genome sequences of 42 species were surveyed. Surface plasmon resonance (SPR) was performed with peptides to characterise the binding site of β₂GPI for LPS. β₂GPI could be identified in most tested vertebrates with a high overall amino acid homology of 80% or more in mammals. SPR revealed that a synthesised peptide (LAFWKTDA) from domain V of β₂GPI was able to compete for binding of β₂GPI to LPS. The AFWKTDA sequence was completely conserved in all mammals. The peptide containing the LPS binding site attenuated the inhibition by β₂GPI in a cellular model of LPS-induced tissue factor expression. Other important sites, such as the binding site for anionic phospholipids and the antiphospholipid antibody binding epitope, were also preserved. β₂GPI is highly conserved across the animal kingdom, which suggests that the function of β₂GPI may be more important than anticipated.
authors.affiliation: Department of Experimental Vascular Medicine, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
authors.forename: Çetin
authors.initials: Ç
authors.lastname: Ağar
authors.forename: Philip G
authors.initials: PG
authors.lastname: de Groot
authors.forename: J Arnoud
authors.initials: JA
authors.lastname: Marquart
authors.forename: Joost C M
authors.initials: JC
authors.lastname: Meijers
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites / Q000235:genetics; D001667:Binding, Competitive; D002478:Cells, Cultured; D017124:Conserved Sequence / Q000235:genetics; D015536:Down-Regulation / Q000187:drug effects; D019143:Evolution, Molecular; D006801:Humans; D008070:Lipopolysaccharides / Q000378:metabolism*; D008969:Molecular Sequence Data; D009000:Monocytes / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D010446:Peptide Fragments / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D016415:Sequence Alignment; D020349:Surface Plasmon Resonance; D013925:Thromboplastin / Q000235:genetics / Q000378:metabolism; D053482:beta 2-Glycoprotein I / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology
chemical_list: D008070:Lipopolysaccharides; D010446:Peptide Fragments; D053482:beta 2-Glycoprotein I; D013925:Thromboplastin