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Investigating Single Molecule Adhesion by Atomic Force Spectroscopy
Published on: February 27, 2015
Localization of the lipopolysaccharide-binding protein in phospholipid membranes by atomic force microscopy
Stefanie Roes1, Florian Mumm, Ulrich Seydel
1Research Center Borstel, Leibniz-Center for Medicine and Biological Sciences, Division of Biophysics, Parkallee 10, Borstel 23845, Germany.
Insights
Lipopolysaccharide-binding protein (LBP) organizes lipid membranes and facilitates the aggregation of lipopolysaccharides (LPS), a key step in immune cell activation. This protein mediates membrane fusion, influencing how cells respond to endotoxins.
Area of Science:
- Immunology
- Biophysics
- Cell Biology
Background:
- Lipopolysaccharides (LPS), also known as endotoxins, are potent activators of host immunocompetent cells through transmembrane signaling.
- The precise role of Lipopolysaccharide-binding protein (LBP) in mediating this cellular activation process requires further elucidation.
Purpose of the Study:
- To investigate the function of Lipopolysaccharide-binding protein (LBP) in the activation of immunocompetent cells by lipopolysaccharides (LPS).
- To characterize the lateral organization and interaction of LBP within model cell membranes upon LPS aggregation.
Main Methods:
- Mimicking cellular cytoplasmic membranes using lipid liposomes adsorbed on mica.
- Utilizing atomic force microscopy (AFM) to characterize LBP organization and LPS interactions.
- Employing cantilever tips functionalized with anti-LBP antibodies for single-molecule localization.
Main Results:
- LBP molecules were localized within lipid membranes, forming clusters and inducing cross-linking of lipid bilayers at higher concentrations.
- Addition of LPS to LBP-containing liposomes resulted in the formation of distinct LPS domains.
- Anti-LBP antibodies inhibited the formation of LPS domains, indicating LBP's crucial role.
Conclusions:
- Lipopolysaccharide-binding protein (LBP) mediates the fusion of lipid membranes and lipopolysaccharide (LPS) aggregates.
- LBP plays a critical role in organizing membrane components and facilitating LPS interactions, influencing cellular responses to endotoxins.
Abstract:
Lipopolysaccharides (LPS; endotoxin) activate immunocompetent cells of the host via a transmembrane signaling process. In this study, we investigated the function of the LPS-binding protein (LBP) in this process. The cytoplasmic membrane of the cells was mimicked by lipid liposomes adsorbed on mica, and the lateral organization of LBP in these membranes and its interaction with LPS aggregates were characterized by atomic force microscopy. Using cantilever tips functionalized with anti-LBP antibodies, single LBP molecules were localized in the membrane at low concentrations. At higher concentrations, LBP formed clusters of several molecules and caused cross-linking of lipid bilayers. The addition of LPS to LBP-containing liposomes led to the formation of LPS domains in the membranes, which could be inhibited by anti-LBP antibodies. Thus, LBP mediates the fusion of lipid membranes and LPS aggregates.
