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Structure and function of β2-glycoprotein I: with special reference to the interaction with phospholipidFaculty of Science, University of Osaka, Toyonaka
Faculty of Science, University of Osaka, Toyonaka
National Cardiovascular Center Research Institute, Suita
Institute for Enzyme Research, University of Tokushima, Tokushima, Japan β2-Glycoprotein I (β2-GPI) is a cofactor in the recognition of a phospholipid antigen, cardiolipin, by anticardiolipin antibodies in autoimmune diseases such as systemic lupus erythematosus. We examined the interaction of various forms of bovine β2-GPI, such as its intact form, desialylated form (Asialo β2-GPI), N-terminal domain (domain 1) and the modified forms of β2-GPI and Asialo β2-GPI with nicks in their C-terminal domains (domain 5), with phospholipid liposomes under different conditions of pH and ionic strength. We found that at neutral pH and low ionic strength β2-GPI bound to liposome membranes containing cardiolipin with a dissociation constant (Kd) of 10-8 M. Phosphatidylglycerol, phosphatidylserine, phosphatidic acid or phosphatidylinositol bound to β2-GPI, but phosphatidylcholine did not. We also found that domain 1 and Asialo β2-GPI bound to cardiolipin with Kd values of 10-6 and 10-8 M, respectively, At neutral pH and both low and high ionic strengths, the affinities of nicked forms of β 2-GPI and Asialo β2-GPI for cardiolipin were lower than those of intact forms but similar to that of domain 1.
Key Words: β2-GPI • Modified forms • Interaction • Phospholipid
Lupus, Vol. 4, No. 1 suppl,
S3-S5 (1994) |
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