The role of scaffolding proteins in the assembly of the small, single-stranded DNA virus φX174

Terje Dokland, Ricardo A. Bernal, April Burch, Sergei Pletnev, Bentley A. Fane, Michael G. Rossmann

Research output: Contribution to journalArticlepeer-review

74 Scopus citations


An empty precursor particle called the procapsid is formed during assembly of the single-stranded DNA bacteriophage φX174. Assembly of the φX174 procapsid requires the presence of the two scaffolding proteins, D and B, which are structural components of the procapsid, but are not found in the mature virion. The X-ray crystallographic structure of a 'closed' procapsid particle has been determined to 3.5 Å resolution. This structure has an external scaffold made from 240 copies of protein D, 60 copies of the internally located B protein, and contains 60 copies of each of the viral structural proteins F and G, which comprise the shell and the 5-fold spikes, respectively. The F capsid protein has a similar conformation to that seen in the mature virion, and differs from the previously determined 25 Å resolution electron microscopic reconstruction of the 'open' procapsid, in which the F protein has a different conformation. The D scaffolding protein has a predominantly α-helical fold and displays remarkable conformational variability. We report here an improved and refined structure of the closed procapsid and describe in some detail the differences between the four independent D scaffolding proteins per icosahedral asymmetric unit, as well as their interaction with the F capsid protein. We re-analyze and correct the comparison of the closed procapsid with the previously determined cryo-electron microscopic image reconstruction of the open procapsid and discuss the major structural rearrangements that must occur during assembly. A model is proposed in which the D proteins direct the assembly process by sequential binding and conformational switching.

Original languageEnglish (US)
Pages (from-to)595-608
Number of pages14
JournalJournal of Molecular Biology
Issue number4
StatePublished - May 14 1999


  • Bacteriophage φX174
  • Morphogenesis
  • Procapsid
  • Scaffolding proteins
  • Three-dimensional structure

ASJC Scopus subject areas

  • Biophysics
  • Structural Biology
  • Molecular Biology


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