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Structural polymorphism correlated to surface charge in filamentous bacteriophages
S Bhattacharjee1, M J Glucksman, L Makowski
1Department of Biochemistry and Molecular Biophysics, College of Physicians and Surgeons, Columbia University, New York, New York 10032.
Abstract:
Fiber diffraction studies are used to demonstrate that changes in the helical symmetry of the protein coat of filamentous bacterial viruses fd and M13 are correlated with changes in the surface charge. Comparison of the structure of M13 and fd at pH 2 and 8 indicate that surface charge affects both the helical symmetry and flexibility of the virions. The changes in helical symmetry are similar in magnitude to that observed in the Pseudomanas phage Pf1 and probably reflect an inocuous side effect of the particle flexibility required for protection of the virus particles from damage due to shear. The magnitude of the observed changes in helical symmetry appears to be limited to that which can occur without repacking of the interfaces between the alpha-helices making up the viral protein coat.
Insights
Changes in surface charge alter the helical symmetry and flexibility of filamentous viruses like M13 and fd. These structural modifications are essential for viral particle flexibility and protection against shear forces.
Area of Science:
- Structural biology
- Virology
- Biophysics
Background:
- Filamentous bacterial viruses (e.g., fd and M13) possess a protein coat with helical symmetry.
- Surface charge of viral particles can influence their structural properties.
Purpose of the Study:
- To investigate the correlation between surface charge and helical symmetry in fd and M13 viruses.
- To understand how surface charge affects virion flexibility and structural integrity.
Main Methods:
- Fiber diffraction studies were employed to analyze the structure of fd and M13 viruses.
- Comparative analysis of viral structures at different pH levels (pH 2 and 8) to probe surface charge effects.
Main Results:
- A direct correlation was observed between changes in surface charge and alterations in helical symmetry of the viral protein coat.
- Surface charge significantly impacts both helical symmetry and flexibility of M13 and fd virions.
- Observed changes in helical symmetry are comparable to those in Pseudomonas phage Pf1 and are within limits that do not disrupt the viral coat's alpha-helix interfaces.
Conclusions:
- Surface charge is a critical determinant of helical symmetry and flexibility in filamentous viruses.
- The observed structural flexibility is likely an adaptive trait for protecting viral particles from shear-induced damage.
- Structural changes are accommodated without compromising the integrity of the viral protein coat's inter-helical interfaces.