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Major proteins of the Escherichia coli outer cell envelope membrane as bacteriophage receptors
Abstract:
Three Escherichia coli phages, TuIa, TuIb, and TuII, were isolated from local sewage. We present evidence that they use the major outer membrane proteins Ia, Ib, and II, respectively, as receptors. In all cases the proteins, under the experimental conditions used, required lipopolysaccharide to exhibit their receptor activity. For proteins Ia and II, an approximately two- to eightfold molar excess of lipopolysaccharide (based on one diglucosamine unit) was necessary to reach maximal receptor activity. Lipopolysaccharide did not appear to possess phage-binding sites. It seemed that the lipopolysaccharide requirement reflected a protein-lipopolysaccharide interaction in vivo, and lipopolysaccharide may thus cause the specific localization of these proteins. Inactivation of phage TuII by a protein II-lipopolysaccharide complex was reversible as long as the complex was in solution. Precipitation of the complex with Mg2+ led to irreversible phage inactivation with an inactivation constant (37 degrees C)K = 7 X 10-2 ml/min per microgram. With phages TuIa and TuIb and their respective protein-lipopolysaccharide complexes, only irreversible inactivation was found at 37 degrees C. The activity of the three proteins as phage receptors shows that part of them must be located at the cells surface. In addition, the association of proteins Ia and Ib with the murein layer of the cell envelope makes this pair trans-membrane proteins.
Insights
Three Escherichia coli phages use outer membrane proteins as receptors, requiring lipopolysaccharide for activity. This interaction influences protein localization and phage inactivation, revealing insights into bacterial cell surface structures.
Area of Science:
- Microbiology
- Bacteriology
- Virology
Background:
- Escherichia coli phages are viruses that infect bacteria.
- Outer membrane proteins (OMPs) and lipopolysaccharides (LPS) are key components of the Gram-negative bacterial cell envelope.
- Phage-host interactions are crucial for understanding bacterial infection and phage therapy.
Purpose of the Study:
- To identify the specific receptors used by three isolated Escherichia coli phages (TuIa, TuIb, TuII).
- To investigate the role of outer membrane proteins and lipopolysaccharide in phage binding and inactivation.
- To elucidate the structural basis of phage-receptor interactions at the bacterial cell surface.
Main Methods:
- Isolation and characterization of three Escherichia coli phages from sewage.
- Identification of major outer membrane proteins (Ia, Ib, II) as phage receptors.
- Experimental analysis of the requirement for lipopolysaccharide in receptor activity.
- Investigation of phage inactivation kinetics with protein-lipopolysaccharide complexes.
Main Results:
- Phages TuIa, TuIb, and TuII utilize outer membrane proteins Ia, Ib, and II, respectively, as receptors.
- Lipopolysaccharide is essential for the receptor activity of these outer membrane proteins.
- Phage inactivation by protein-lipopolysaccharide complexes can be reversible or irreversible depending on complex solubility and precipitation.
- Proteins Ia and Ib are identified as trans-membrane proteins associated with the murein layer.
Conclusions:
- Outer membrane proteins Ia, Ib, and II are specific receptors for phages TuIa, TuIb, and TuII.
- Lipopolysaccharide plays a critical role in mediating phage binding by stabilizing outer membrane protein receptor function.
- The interaction between phages, outer membrane proteins, and lipopolysaccharide provides insights into bacterial cell envelope structure and phage-host dynamics.