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Association of the major coat protein of fd bacteriophage with phospholipid vesicles
Abstract:
The association of the major coat protein of fd bacteriophage with a phospholipid bilayer was investigated by analyzing the protein's susceptibility to proteolysis and its circular dichroism spectrum when incorporated into single-walled phospholipid vesicles. In the limits tested, this association appeared to be independent of the mass ratio of protein to lipid and of vesicle size, phospholipid composition, and method of preparation. The circular dichroism data are consistent with a similar "membrane-bound" conformation for all cases of vesicle-associated coat protein and for deoxycholate micelle-associated coat protein. Proteolysis of coat protein associated with deoxycholate micelles and with phospholipid vesicles defined the central hydrophobic core presumed to represent that portion of the protein which associates with membrane bilayers in vivo. The isolated core, which assumed a predominantly beta-type conformation in detergent solution, maintained a beta conformation when associated with a vesicle phospholipid bilayer.
Insights
The fd bacteriophage coat protein binds to phospholipid bilayers, forming a stable beta-conformation. This membrane association is independent of vesicle properties and preparation methods.
Area of Science:
- Biochemistry
- Structural Biology
- Molecular Biophysics
Background:
- The major coat protein of fd bacteriophage is essential for viral assembly and infection.
- Understanding its interaction with phospholipid bilayers is crucial for elucidating viral membrane fusion mechanisms.
Purpose of the Study:
- To investigate the association of fd bacteriophage coat protein with phospholipid bilayers.
- To determine the structural conformation of the coat protein upon membrane association.
- To identify the specific regions of the protein involved in membrane interaction.
Main Methods:
- Proteolysis susceptibility assays to probe protein structure and accessibility.
- Circular dichroism (CD) spectroscopy to analyze protein secondary structure.
- Incorporation of the protein into single-walled phospholipid vesicles and deoxycholate micelles.
Main Results:
- The coat protein's association with phospholipid vesicles was independent of lipid ratio, vesicle size, and preparation method.
- Circular dichroism data indicated a consistent membrane-bound conformation across different conditions.
- Proteolysis studies identified a central hydrophobic core responsible for membrane bilayer association.
- This hydrophobic core maintained a predominantly beta-conformation when associated with vesicles.
Conclusions:
- The fd bacteriophage coat protein adopts a stable, predominantly beta-type conformation when associated with phospholipid bilayers.
- The central hydrophobic region is key to the protein's membrane interaction.
- These findings provide insights into the structural basis of viral coat protein-membrane interactions.