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Directed Protein Packaging within Outer Membrane Vesicles from Escherichia coli: Design, Production and Purification
Published on: November 16, 2016
Stepwise expansion of the bacteriophage ϕ6 procapsid: possible packaging intermediates
Daniel Nemecek1, Naiqian Cheng, Jian Qiao
1National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
Journal of Molecular Biology
|October 25, 2011
Summary
Bacteriophage ϕ6 procapsid expansion is a cooperative process linked to RNA packaging. Structural intermediates observed suggest mature capsid formation requires internal genome pressure.
Area of Science:
- Structural biology
- Virology
- Molecular biology
Background:
- The bacteriophage ϕ6 procapsid transforms from a compact state to a larger, spherical mature capsid during genome packaging.
- This expansion is proposed to be a stepwise process, with each stage facilitating the binding of specific RNA segments.
Purpose of the Study:
- To investigate the transformability of the bacteriophage ϕ6 procapsid.
- To understand the relationship between procapsid expansion and RNA packaging.
- To characterize the structural intermediates involved in capsid maturation.
Main Methods:
- Cryo-electron microscopy (cryo-EM) reconstructions of procapsids.
- Cryo-electron tomography (cryo-ET) analysis of capsid structures.
- Induction of procapsid expansion via acidification, heating, and elevated salt concentration.
- Analysis of mature capsids upon RNA release.
Main Results:
- Procapsid expansion induced by various treatments resulted in a consistent partially expanded intermediate state.
- Capsid vertices exhibited a cooperative transition between compact and expanded states.
- Mature capsids, upon RNA release, reverted to intermediate states, suggesting genome pressure is crucial for the final conformation.
- Two distinct expansion intermediates were observed, supporting a multi-step packaging model.
Conclusions:
- Bacteriophage ϕ6 procapsid expansion is a cooperative, multi-step process.
- The mature capsid structure is stabilized by the outward pressure of the packaged genome.
- Observed intermediates align with a model of sequential RNA packaging and capsid expansion.
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