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Updated: Aug 9, 2026
Using Scaffold Liposomes to Reconstitute Lipid-proximal Protein-protein Interactions In Vitro
Published on: January 11, 2017
Interaction of bacterial lipopolysaccharide with mouse surfactant protein C inserted into lipid vesicles
L Augusto1, K Le Blay, G Auger
1Endotoxin Group, Unité Mixte de Recherche-8619 of the National Center for Scientific Research, University of Paris-Sud, 91405 Orsay, France.
Abstract:
Infection of the respiratory tract is a frequent cause of lung pathologies, morbidity, and death. When bacterial endotoxin [lipopolysaccharide (LPS)] reaches the alveolar spaces, it encounters the lipid-rich surfactant that covers the epithelium. Although binding of hydrophilic surfactant protein (SP) A and SP-D with LPS has been established, nothing has been reported to date on possible cross talks between LPS and hydrophobic SP-B and SP-C. We designed a new binding technique based on the incorporation of surfactant components to lipid vesicles and the separation of unbound from vesicle-bound LPS on a density gradient. We found that among the different hydrophobic components of mouse surfactant separated by gel filtration or reverse-phase HPLC, only SP-C exhibited the capacity to bind to a tritium-labeled LPS. The binding of LPS to vesicles containing SP-C was saturable, temperature dependent, related to the concentrations of SP-C and LPS, and inhibitable by distinct unlabeled LPSs. Unlike SP-A and SP-D, the binding of SP-C to LPS did not require calcium ions. This LPS binding capacity of SP-C may represent another antibacterial defense mechanism of the lung.
Insights
Lung surfactant protein C (SP-C) binds bacterial lipopolysaccharide (LPS) in the alveoli. This novel finding suggests SP-C plays a direct role in the lung's defense against bacterial endotoxins.
Area of Science:
- Pulmonary immunology
- Biochemistry
- Microbiology
Background:
- Respiratory tract infections cause significant lung disease and mortality.
- Bacterial lipopolysaccharide (LPS) in alveolar spaces interacts with lung surfactant.
- The interaction between LPS and hydrophobic surfactant proteins (SPs) like SP-B and SP-C is largely uncharacterized.
Purpose of the Study:
- To investigate the potential binding interactions between lipopolysaccharide (LPS) and hydrophobic surfactant proteins (SPs).
- To determine if surfactant protein C (SP-C) binds to bacterial LPS.
Main Methods:
- Lipid vesicles incorporating surfactant components were used to study binding.
- Separation of vesicle-bound from unbound LPS was achieved using density gradient ultracentrifugation.
- Tritium-labeled LPS was utilized to quantify binding interactions.
- Hydrophobic surfactant proteins were purified using gel filtration and reverse-phase HPLC.
Main Results:
- Surfactant protein C (SP-C) demonstrated a direct binding capacity to lipopolysaccharide (LPS).
- SP-C binding to LPS was concentration-dependent, saturable, and temperature-sensitive.
- Calcium ions were not required for SP-C to bind LPS, unlike hydrophilic SPs.
- Binding was inhibited by unlabeled LPS, confirming specificity.
Conclusions:
- Hydrophobic surfactant protein C (SP-C) directly binds bacterial lipopolysaccharide (LPS).
- This interaction represents a previously unrecognized mechanism of innate antibacterial defense in the lung.
- SP-C's LPS-binding capability may contribute to reducing endotoxin-induced lung injury.
