Solution Structure of Human and Bovine β2-Glycoprotein I Revealed by Small-angle X-ray Scattering

β2-Glycoprotein I (β2GPI) is a highly glycosylated phospholipid-binding plasma protein comprised of four complement control protein (CCP) domains and a distinct fifth domain. The structural organisation of human and bovine β2GPI in aqueous solution was studied by small-angle X-ray scattering (SAXS). Low-resolution models that match the SAXS experimental data best were independently constructed by three different ab initio 3D-reconstruction algorithms. Similar elongated S-shaped models with distinct side-arms, which were correlated to the position of the carbohydrate chains, were restored from all three algorithms. Due to an additional glycosylation site located on the CCP2 domain of bovine β2GPI a small change in the characteristic SAXS parameters was observed, which coincided with results obtained from SDS–PAGE. In comparison to the human analogue the corresponding restored low-resolution models displayed a similar S-shape with less bending in the middle part.