4JPP : Bacteriophage phiX174 H protein residues 143-282

  • Bentley A Fane (Contributor)
  • Lei Sun (Contributor)
  • Lindsey N. Young (Contributor)
  • Xinzheng Zhang (Contributor)
  • Sergei P. Boudko (Contributor)
  • Andrei Fokine (Contributor)
  • Michael G. Rossmann (Contributor)



Experimental Technique/Method:X-RAY DIFFRACTION
Classification:VIRAL PROTEIN
Release Date:2013-12-11
Deposition Date:2013-03-19
Revision Date:2014-01-15#2014-01-22
Molecular Weight:79768.23
Macromolecule Type:Protein
Residue Count:700
Atom Site Count:5027

Prokaryotic viruses have evolved various mechanisms to transport their genomes across bacterial cell walls. Many bacteriophages use a tail to perform this function, whereas tail-less phages rely on host organelles. However, the tail-less, icosahedral, single-stranded DNA ΦX174-like coliphages do not fall into these well-defined infection processes. For these phages, DNA delivery requires a DNA pilot protein. Here we show that the ΦX174 pilot protein H oligomerizes to form a tube whose function is most probably to deliver the DNA genome across the host's periplasmic space to the cytoplasm. The 2.4 Å resolution crystal structure of the in vitro assembled H protein's central domain consists of a 170 Å-long α-helical barrel. The tube is constructed of ten α-helices with their amino termini arrayed in a right-handed super-helical coiled-coil and their carboxy termini arrayed in a left-handed super-helical coiled-coil. Genetic and biochemical studies demonstrate that the tube is essential for infectivity but does not affect in vivo virus assembly. Cryo-electron tomograms show that tubes span the periplasmic space and are present while the genome is being delivered into the host cell's cytoplasm. Both ends of the H protein contain transmembrane domains, which anchor the assembled tubes into the inner and outer cell membranes. The central channel of the H-protein tube is lined with amide and guanidinium side chains. This may be a general property of viral DNA conduits and is likely to be critical for efficient genome translocation into the host.
Date made available2013

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