title: The Staphylococcus aureus pathogenicity island 1 protein gp6 functions as an internal scaffold during capsid size determination.
abstract: Staphylococcus aureus pathogenicity island 1 (SaPI1) is a mobile genetic element that carries genes for several superantigen toxins. SaPI1 is normally stably integrated into the host genome but can become mobilized by "helper" bacteriophage 80α, leading to the packaging of SaPI1 genomes into phage-like transducing particles that are composed of structural proteins supplied by the helper phage but having smaller capsids. We show that the SaPI1-encoded protein gp6 is necessary for efficient formation of small capsids. The NMR structure of gp6 reveals a dimeric protein with a helix-loop-helix motif similar to that of bacteriophage scaffolding proteins. The gp6 dimer matches internal densities that bridge capsid subunits in cryo-electron microscopy reconstructions of SaPI1 procapsids, suggesting that gp6 acts as an internal scaffolding protein in capsid size determination.
authors.affiliation: Department of Microbiology, University of Alabama at Birmingham, Birmingham, AL 35294, USA.
authors.forename: Altaira D
authors.initials: AD
authors.lastname: Dearborn
authors.forename: Michael S
authors.initials: MS
authors.lastname: Spilman
authors.forename: Priyadarshan K
authors.initials: PK
authors.lastname: Damle
authors.forename: Jenny R
authors.initials: JR
authors.lastname: Chang
authors.forename: Eric B
authors.initials: EB
authors.lastname: Monroe
authors.forename: Jamil S
authors.initials: JS
authors.lastname: Saad
authors.forename: Gail E
authors.initials: GE
authors.lastname: Christie
authors.forename: Terje
authors.initials: T
authors.lastname: Dokland
mesh_terms: D000595:Amino Acid Sequence; D002213:Capsid / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D036022:Capsid Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D003198:Computer Simulation; D044404:Genomic Islands / Q000235:genetics; D008954:Models, Biological; D008958:Models, Molecular; D053141:Organelle Size / Q000235:genetics*; D030781:Organisms, Genetically Modified; D017510:Protein Folding; D055503:Protein Multimerization / Q000235:genetics / Q000502:physiology; D020836:Protein Structure, Quaternary; D013211:Staphylococcus aureus / Q000235:genetics / Q000472:pathogenicity / Q000502:physiology / Q000648:ultrastructure; D019065:Virus Assembly / Q000235:genetics
chemical_list: D036022:Capsid Proteins