Binding analysis of domains I, IV, and V of β₂GPI. Binding of domain I to domains IV and V was investigated with surface plasmon resonance. Domain I of β₂GPI (150 RU) was immobilized to a CM5 sensor chip, and increasing concentrations (25-200nM) of domain IV or domain V were applied to the chip. Binding of domain V to domain I in a concentration-dependent manner was observed. No detectable interaction could be observed between domain IV and domain I.