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Membrane orientation and antigenic peptides of an immunoprotective 74 kDa Plasmodium knowlesi glycoprotein
Abstract:
Vaccination trials have shown that a purified, 74 kDa glycoprotein, GP74, isolated from the host cell membrane of Plasmodium knowlesi-infected rhesus erythrocytes, can provide protective immunity against P. knowlesi malaria. We have extended this work by a tryptic peptide analysis of the disposition of GP74 in the host cell membrane. Of the 18 peptides characterized by high-performance liquid chromatography only four were accessible to lactoperoxidase-catalyzed radioiodination of non-leaky, schizont-infected host cells from the extracellular space. Metabolic labeling with radioactive glucosamine indicates that two of the surface exposed peptides are glycopeptides, and one of these, peptide 12 appears to carry a dominant antigenic site, according to its reactivity with immunoglobulin from sera of monkeys protected against P. knowlesi malaria.
Insights
A key Plasmodium knowlesi malaria vaccine target, glycoprotein 74 (GP74), has surface-exposed regions on infected red blood cells. Peptide 12 on GP74 is a dominant antigenic site, crucial for protective immunity.
Area of Science:
- Malariology
- Immunology
- Parasitology
Background:
- Vaccination with Plasmodium knowlesi glycoprotein 74 (GP74) confers protection against P. knowlesi malaria.
- Understanding GP74's location on infected host cells is vital for vaccine development.
Purpose of the Study:
- To analyze the disposition of GP74 within the host cell membrane using tryptic peptide analysis.
- To identify surface-exposed regions of GP74 accessible from the extracellular space.
Main Methods:
- Tryptic peptide analysis of GP74.
- High-performance liquid chromatography (HPLC) for peptide characterization.
- Lactoperoxidase-catalyzed radioiodination to identify surface-exposed peptides.
- Metabolic labeling with radioactive glucosamine to identify glycopeptides.
Main Results:
- 18 GP74 peptides were characterized.
- Four peptides were accessible from the extracellular space.
- Two surface-exposed peptides were identified as glycopeptides.
- Peptide 12, a surface-exposed glycopeptide, demonstrated reactivity with antibodies from protected monkeys, indicating a dominant antigenic site.
Conclusions:
- GP74 has surface-exposed regions on Plasmodium knowlesi-infected erythrocytes.
- Peptide 12 represents a major antigenic site on GP74, likely contributing to protective immunity.
- These findings support GP74 as a viable target for malaria vaccine development.