Oxidation and biotinylation of beta 2 glycoprotein I glycan chains induce an increase in its affinity for anionic phospholipids similar to that obtained by the addition of anti-beta 2 glycoprotein I or anti-cardiolipin antibodies

Binding of beta 2 glycoprotein I (β2GPI) to apoptotic cells plays a key role in the opsonization of apoptotic bodies and the formation of antiphospholipids antibodies. Here, we describe the binding of β2GPI to apoptotic cells using β2GPI labelled with biotin-hydrazide (β2GPI-bh) after oxidation of its glycan chains. Flow cytometry analyses and confocal microscopy showed that β2GPI-bh, contrary to native β2GPI, bound to apoptotic cells, either permeable or non-permeable to propidium iodide (PI), as did annexin-V-FITC. But, in the absence of divalent ions, β2GPI-bh, contrary to annexin V, was still able to bind to apoptotic cells. Binding equilibrium studies, performed on solid-state anionic phospholipids (AnPL), revealed that β2GPI-bh had a greater apparent affinity for AnPL than native β2GPI. In presence of the anti-β2GPI mAb 8C3, the ability of native β2GPI to bind to AnPL was increased and binding to apoptotic PI+ and PI− CEM cells was observed whereas binding of β2GPI-bh was barely affected by the addition of 8C3. However, the 8C3-enhanced ability of native β2GPI to bind to AnPL was still weaker than that of β2GPI-bh. It is not clear why the oxidation and biotinylation of glycan chains of β2GPI increases its affinity for AnPL, but it seems that if such oxidative process occurs naturally, it could participate in enhancing antiphospholipid formation.