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Two asialoglycoprotein receptor polypeptides in human hepatoma cells
The Journal of Biological Chemistry
|August 25, 1987
Summary
Researchers identified a new glycoprotein, H2, homologous to the asialoglycoprotein receptor H1. H2 is synthesized similarly to H1 and functions as a galactose-binding protein, though it is less abundant.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- The asialoglycoprotein receptor (H1) mediates endocytosis of desialylated glycoproteins.
- A homologous membrane glycoprotein, H2, was identified but its relationship to H1 and function were unclear.
Purpose of the Study:
- To investigate the relationship between H2 and H1.
- To determine the role of H2 in receptor-mediated endocytosis.
- To characterize the synthesis and cell surface expression of H2.
Main Methods:
- Generated specific anti-peptide antibodies for H1 and H2.
- Utilized metabolic labeling and immunoadsorption in HepG2 cells.
- Performed trypsin and neuraminidase digestion assays.
- Purified H1 and H2 via affinity chromatography on galactose-agarose.
Main Results:
- H2 shares similar biosynthesis and processing pathways with H1.
- Both H1 and H2 have a half-life of approximately 12 hours.
- 50-60% of H1 and H2 are cell surface-expressed at steady state.
- H2 is a galactose-binding protein and exists in a 5-6 fold lower abundance than H1.
Conclusions:
- H2 is a distinct galactose-binding protein homologous to H1.
- H2's lower abundance may explain its delayed discovery.
- H2 likely plays a role in glycoprotein endocytosis, similar to H1.