Comparison of LC-MS surveys of β₂GPI. LC-MS analyses of open and circular β₂GPI. The molecular masses of detected tryptic peptides are indicated. Comparison of these 2 analyses shows that in the open conformation of β₂GPI (top panel) cleavage has taken place of the amino acids Lys19, Arg39, Arg43 (domain I), Lys305, and Lys317 (domain V) indicated by black arrows, whereas they are not or less visible in the circular conformation of β₂GPI (bottom panel) indicated by white arrows.