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Elife. 2017 Oct 6;6. pii: e30822. doi: 10.7554/eLife.30822.

Competing scaffolding proteins determine capsid size during mobilization of Staphylococcus aureus pathogenicity islands.

Author information

Protein Expression Laboratory, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, United States.
Department of Microbiology and Immunology, Virginia Commonwealth University, Richmond, United States.
Department of Microbiology, University of Alabama, Birmingham, United States.
Direct Electron, San Diego, United States.
Biological Science Imaging Resource, Florida State University, Tallahassee, United States.
Contributed equally


Staphylococcus aureus pathogenicity islands (SaPIs), such as SaPI1, exploit specific helper bacteriophages, like 80α, for their high frequency mobilization, a process termed 'molecular piracy'. SaPI1 redirects the helper's assembly pathway to form small capsids that can only accommodate the smaller SaPI1 genome, but not a complete phage genome. SaPI1 encodes two proteins, CpmA and CpmB, that are responsible for this size redirection. We have determined the structures of the 80α and SaPI1 procapsids to near-atomic resolution by cryo-electron microscopy, and show that CpmB competes with the 80α scaffolding protein (SP) for a binding site on the capsid protein (CP), and works by altering the angle between capsomers. We probed these interactions genetically and identified second-site suppressors of lethal mutations in SP. Our structures show, for the first time, the detailed interactions between SP and CP in a bacteriophage, providing unique insights into macromolecular assembly processes.


S. aureus pathogenicity island 1 (SaPI1); Staphylococcus aureus; bacteriophage 80alpha; biophysics; cryo-electron microscopy; infectious disease; microbiology; structural biology; three-dimensional reconstruction; virus structure and assembly

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