β2-glycoprotein 1, also known as beta-2 glycoprotein 1 and Apolipoprotein H (Apo-H), is a 38 kDa multifunctional plasma protein that in humans is encoded by the APOH gene. One of its functions is to bind cardiolipin. When bound, the structure of cardiolipin and β2-GP1 both undergo large changes in structure.[6] Within the structure of Apo-H is a stretch of positively charged amino acids (protein sequence positions 282-287), Lys-Asn-Lys-Glu-Lys-Lys, are involved in phospholipid binding (see image on right). β2-GP1 has a complex involvement in agglutination. It appears to alter adenosine diphosphate (ADP)-mediated agglutination of platelets. Normally, β2-GP1 assumes an anticoagulation activity in serum (by inhibiting coagulation factors); however, changes in blood factors can result in a reversal of that activity. Although previously referred to as apolipoprotein H, it is not present in appreciable quantities in the lipoprotein fractions, so ApoH is therefore thought to be a misnomer.