Electron microscopy analysis of β₂GPI. Purified human plasma β₂GPI was visualized with electron microscopy in the absence or presence of gold-labeled (black dots) LPS or albumin. Magnifications of purified plasma β₂GPI show a circular conformation (A). Purified plasma β₂GPI in the presence of gold-labeled LPS shows on magnification an open fishhook-like shape of β₂GPI (B), where LPS is bound to domain V of β₂GPI, as indicated with the white arrows. Incubation of plasma β₂GPI with gold-labeled albumin, as a control, does not induce a conformational change of β₂GPI (C). White bar represents 10 nm.