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Hepatitis B virus surface antigen binds to apolipoprotein H
H Mehdi1, M J Kaplan, F Y Anlar
1Department of Immunology/Microbiology, Rush-Presbyterian-St. Luke's Medical Center, Chicago, Illinois 60612-3864.
Journal of Virology
|April 1, 1994
Summary
Hepatitis B surface antigen binds to apolipoprotein H (apo H), a serum protein found on lipoproteins. This interaction, requiring disulfide bonds in apo H, may facilitate hepatitis B virus entry into liver cells.
Area of Science:
- Hepatology
- Virology
- Biochemistry
Background:
- Previous studies showed human liver plasma membranes bind recombinant hepatitis B surface antigen (rHBsAg).
- The specific binding protein on liver membranes was not previously identified.
Purpose of the Study:
- To identify the 46-kDa rHBsAg-binding protein from human liver plasma membranes.
- To investigate the nature and characteristics of this binding protein and its interaction with HBsAg.
Main Methods:
- Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) to separate membrane proteins.
- Ligand-blotting technique to detect rHBsAg binding proteins.
- Buffer extraction, serum and lipoprotein isolation, and cDNA expression for protein identification and characterization.
Main Results:
- A 46-kDa peripherally bound protein was identified as apolipoprotein H (apo H), also known as beta 2-glycoprotein I.
- Apo H, found in serum and associated with chylomicrons and high-density lipoproteins, binds both recombinant and serum-derived HBsAg.
- Binding is saturable, requires the S protein of HBsAg, and is inhibited by excess HBsAg or antibodies. Disulfide bonds in apo H are crucial for binding.
Conclusions:
- Apolipoprotein H is a key serum protein that binds hepatitis B surface antigen.
- The association of apo H with lipoproteins, which target hepatocytes, suggests a potential mechanism for hepatitis B virus entry into liver cells.