Competing scaffolding proteins determine capsid size during mobilization of Staphylococcus aureus pathogenicity islands
Abstract
Staphylococcus aureus pathogenicity islands (SaPIs), such as SaPI1, exploit specific helper bacteriophages, like 80a, 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 80a and SaPI1 procapsids to near-atomic resolution by cryo-electron microscopy, and show that CpmB competes with the 80a 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.
Data availability
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Capsid protein and C-terminal part of scaffolding protein in the Staphylococcus aureus phage 80alpha procapsidPublicly available at the EMBL-EBI EM Data Bank with accession number -EMDB-7030.
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Capsid protein and C-terminal part of scaffolding protein in the Staphylococcus aureus phage 80alpha procapsidPublicly available at the RCSB Protein Data Bank with accession number 6B0X.
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Capsid protein and C-terminal part of CpmB protein in the Staphylococcus aureus pathogenicity island 1 80alpha-derived procapsidPublicly available at the EMBL-EBI EM Data Bank with accession number -EMDB-7035.
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Capsid protein and C-terminal part of CpmB protein in the Staphylococcus aureus pathogenicity island 1 80alpha-derived procapsidPublicly available at the RCSB Protein Data Bank with accession number 6B23.
Article and author information
Author details
Funding
National Institutes of Health (R01 AI083255)
- Terje Dokland
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Copyright
© 2017, Dearborn et al.
This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.
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