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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

1
Protein Expression Laboratory, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, United States.
2
Department of Microbiology and Immunology, Virginia Commonwealth University, Richmond, United States.
3
Department of Microbiology, University of Alabama, Birmingham, United States.
4
Direct Electron, San Diego, United States.
5
Biological Science Imaging Resource, Florida State University, Tallahassee, United States.
#
Contributed equally

Abstract

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.

KEYWORDS:

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

PMID:
28984245
PMCID:
PMC5644958
DOI:
10.7554/eLife.30822
[Indexed for MEDLINE]
Free PMC Article

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