The fifth domain of beta-2-glycoprotein-1 (b2GP-1) is composed of four well-defined anti-parallel beta-strands and two short alpha-helices, as well as a long highly flexible loop. It plays an important role in the binding of b2GP-1 to negatively charged compounds and subsequent capture for binding of anti-b2GP-1 antibodies [1].

1: Identification of the phospholipid-binding site of human beta(2)-glycoprotein I domain V by heteronuclear magnetic resonance. Hoshino M, Hagihara Y, Nishii I, Yamazaki T, Kato H, Goto Y; J Mol Biol. 2000;304:927-939. PMID:11124037