A viral scaffolding protein triggers portal ring oligomerization and incorporation during procapsid assembly

Sci Adv. 2017 Jul 26;3(7):e1700423. doi: 10.1126/sciadv.1700423. eCollection 2017 Jul.


Most double-stranded DNA viruses package genetic material into empty precursor capsids (or procapsids) through a dodecameric portal protein complex that occupies 1 of the 12 vertices of the icosahedral lattice. Inhibiting incorporation of the portal complex prevents the formation of infectious virions, making this step an excellent target for antiviral drugs. The mechanism by which a sole portal assembly is selectively incorporated at the special vertex is unclear. We recently showed that, as part of the DNA packaging process for bacteriophage P22, the dodecameric procapsid portal changes conformation to a mature virion state. We report that preformed dodecameric rings of P22 portal protein, as opposed to portal monomers, incorporate into nascent procapsids, with preference for the procapsid portal conformation. Finally, a novel role for P22 scaffolding protein in triggering portal ring formation from portal monomers is elucidated and validated by incorporating de novo assembled portal rings into procapsids.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Bacteriophage P22 / physiology*
  • Capsid Proteins / chemistry
  • Capsid Proteins / metabolism*
  • Models, Molecular
  • Protein Conformation
  • Protein Multimerization*
  • Spectrum Analysis
  • Viral Proteins / chemistry
  • Viral Proteins / metabolism
  • Virus Assembly*


  • Capsid Proteins
  • Viral Proteins
  • portal protein, bacteriophage P22