Icosahedral bacteriophage Phi X174 forms a tail for DNA transport during infection
Michael Rossmann group (Purdue University) and collaborators
Prokaryotic viruses have evolved various mechanisms to
transport their genomes across bacterial cell walls, barriers that can
contain two lipid bilayers and a peptidoglycan layer. Many bacteriophages
utilize a tail to perform this function, whereas tail-less phages rely on
host organelles, such as plasmid-encoded receptor complexes and pili.
However, phiX174-like bacterial viruses do not fall into either of these
well-defined infection paradigms. To penetrate cells, coliphage phiX174
utilizes 10 to12 copies of its pilot protein H that is monomeric during the
entire particle assembly pathway. Lei Sun from the Rossmann lab at Purdue
University and Ben Fane at the University of Arizona have shown that the
central domain of the H protein assembles into 170-Å long tubes using
data collected at GM/CA @ APS. The tube is constructed of 10 alpha-helices
with their N-terminal region arrayed in a right-handed super-helix coiled
coil and their C-terminal region arrayed in a left-handed super-helix
coiled-coil. They have used genetic and biochemical data to demonstrate that
the tube is essential for infectivity but does not affect in vivo virus
assembly. As there is no evidence for the presence of the tubes in mature
virions by cryo electron microscopy, the monomeric components do not assemble
until the virus recognizes its host. They have also shown that these tubes
span the periplasmic space to transport the viral genome into the host's
cytoplasm. The 23-Å wide central channel of the H protein tubes is
lined with amide and guanidinium side chains. Bioinformatic analyses indicate
that this may be a general property of viral DNA conduits and is likely to be
critical for efficient genome translocation into the host.
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Figure: PhiX174 forms a tail for DNA
transport during infection. One of the spikes of the virus recognizes a
lipopolysaccharide (LPS) molecule in the outer membrane (OM) of the E. coli
cell wall. After attachment, the virus extrudes H proteins and a tail forms
for DNA penetration. The tail tube is shown crossing the periplasmic space,
lodged in between the outer and inner membrane (IM). |
Citation: Sun L, Young LN, Zhang X, Boudko SP, Fokine A,
Zbornik E, Roznowski AP, Molineux IJ, Rossmann MG, Fane BA. Icosahedral
bacteriophage [phi]X174 forms a tail for DNA transport during infection.
Nature. 2014 January 16; 505: 432-435. doi: 10.1038/nature12816
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