Conformational switching by the scaffolding protein D directs the assembly of bacteriophage phiX174

Mol Cell. 2004 Sep 24;15(6):991-7. doi: 10.1016/j.molcel.2004.08.023.


The three-dimensional structure of bacteriophage phiX174 external scaffolding protein D, prior to its interaction with other structural proteins, has been determined to 3.3 angstroms by X-ray crystallography. The crystals belong to space group P4(1)2(1)2 with a dimer in the asymmetric unit that closely resembles asymmetric dimers observed in the phiX174 procapsid structure. Furthermore, application of the crystallographic 4(1) symmetry operation to one of these dimers generates a tetramer similar to the tetramer in the icosahedral asymmetric unit of the procapsid. These data suggest that both dimers and tetramers of the D protein are true morphogenetic intermediates and can form independently of other proteins involved in procapsid morphogenesis. The crystal structure of the D scaffolding protein thus represents the state of the polypeptide prior to procapsid assembly. Hence, comparison with the procapsid structure provides a rare opportunity to follow the conformational switching events necessary for the construction of complex macromolecular assemblies.

Publication types

  • Comparative Study
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Bacteriophage phi X 174 / metabolism*
  • Capsid Proteins / chemistry
  • Capsid Proteins / metabolism
  • Crystallography, X-Ray
  • Dimerization
  • Escherichia coli Proteins / chemistry
  • Escherichia coli Proteins / metabolism*
  • Models, Molecular
  • Protein Conformation
  • Protein Structure, Secondary
  • Ribosomal Proteins / chemistry
  • Ribosomal Proteins / metabolism*


  • Capsid Proteins
  • Escherichia coli Proteins
  • Ribosomal Proteins
  • ribosome-associated protein SRA, Escherichia coli

Associated data

  • PDB/1TX9