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Adhesion of mycoplasmas to eukaryotic cells
Abstract:
Many pathogenic mycoplasmas are surface parasites, adhering to the epithelial linings of the respiratory and urogenital tracts. Since mycoplasmas lack cell walls their plasma membrane comes in close contact with that of their host, allowing exchange of components between the two membranes and possibly fusion. The tight association of the parasite with its host is illustrated in scanning electron micrographs of Mycoplasma pneumoniae and M. gallisepticum adhering to human red blood cells. Specialized structure at the tips of the mycoplasma cells appear to function as attachment organelles. Our main aim has been to chemically define the receptors on the host cell and the binding sites on the mycoplasma cells responsible for adhesion. Glycophorin (the major sialoglycoprotein of human red blood cells) serves as the main or sole receptor for M. gallisepticum whereas M. pneumoniae binds to additional receptors on human red blood cells. Trypsin treatment of M. pneumoniae cells abolishes their ability to attach to human red cells, suggesting the protein nature of the binding sites. M. pneumoniae membranes solubilized by detergents were subjected to affinity chromatography on glycophorin-Sepharose so that membrane components with high affinity for glycophorin could be isolated. The fraction isolated consisted of several proteins (relative molecular mass 25 000 and 45 000). The binding of this fraction to red cells was relatively low but appeared to be specific, as it was inhibited by glycophorin but not by its hydrophobic moiety. The possibility is discussed that the exposure of the binding sites on the mycoplasma cell surface is influenced by the electrochemical ion gradient across the membrane.
Insights
Pathogenic mycoplasmas adhere to host cells via specialized attachment structures. Researchers identified specific proteins on Mycoplasma pneumoniae responsible for binding to host cell receptors like glycophorin.
Area of Science:
- Microbiology
- Cell Biology
- Biochemistry
Background:
- Pathogenic mycoplasmas are surface parasites lacking cell walls, enabling close contact and potential membrane fusion with host cells.
- Mycoplasma adhesion to host epithelial cells is mediated by specialized tip structures, crucial for colonization of respiratory and urogenital tracts.
- Previous studies visualized Mycoplasma pneumoniae and Mycoplasma gallisepticum adhering to human red blood cells, highlighting their attachment mechanisms.
Purpose of the Study:
- To chemically define the specific host cell receptors and mycoplasma binding sites involved in parasite-host adhesion.
- To elucidate the molecular interactions underlying the attachment of Mycoplasma pneumoniae to human red blood cells.
Main Methods:
- Affinity chromatography using glycophorin-Sepharose to isolate Mycoplasma pneumoniae membrane components with high affinity for glycophorin.
- Analysis of isolated membrane proteins using techniques to determine their molecular mass and binding characteristics.
- Inhibition assays using glycophorin and its moieties to confirm the specificity of mycoplasma binding.
Main Results:
- Glycophorin identified as a primary receptor for Mycoplasma gallisepticum and one of several receptors for Mycoplasma pneumoniae on human red blood cells.
- Trypsin treatment of Mycoplasma pneumoniae abolished its attachment to red blood cells, indicating the protein nature of its binding sites.
- Isolated Mycoplasma pneumoniae membrane fractions containing proteins of 25,000 and 45,000 molecular mass showed specific, albeit low, binding to red blood cells, inhibited by glycophorin.
Conclusions:
- Specific protein components of Mycoplasma pneumoniae mediate adhesion to host cell receptors, including glycophorin.
- The binding sites on Mycoplasma pneumoniae are proteinaceous and their exposure may be influenced by the cell's electrochemical ion gradient.
- Understanding these molecular interactions is key to developing strategies against mycoplasma infections.