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PDBsum entry 6ibc
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Contents |
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(+ 0 more)
374 a.a.
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345 a.a.
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References listed in PDB file
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Key reference
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Title
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Cryo-Em structure and in vitro DNA packaging of a thermophilic virus with supersized t=7 capsids.
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Authors
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O.W.Bayfield,
E.Klimuk,
D.C.Winkler,
E.L.Hesketh,
M.Chechik,
N.Cheng,
E.C.Dykeman,
L.Minakhin,
N.A.Ranson,
K.Severinov,
A.C.Steven,
A.A.Antson.
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Ref.
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Proc Natl Acad Sci U S A, 2019,
116,
3556-3561.
[DOI no: ]
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PubMed id
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Note: In the PDB file this reference is
annotated as "TO BE PUBLISHED". The citation details given above have
been manually determined.
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Abstract
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Double-stranded DNA viruses, including bacteriophages and herpesviruses, package
their genomes into preformed capsids, using ATP-driven motors. Seeking to
advance structural and mechanistic understanding, we established in vitro
packaging for a thermostable bacteriophage, P23-45 of Thermus
thermophilus Both the unexpanded procapsid and the expanded mature capsid
can package DNA in the presence of packaging ATPase over the 20 °C to 70 °C
temperature range, with optimum activity at 50 °C to 65 °C. Cryo-EM
reconstructions for the mature and immature capsids at 3.7-Å and 4.4-Å
resolution, respectively, reveal conformational changes during capsid expansion.
Capsomer interactions in the expanded capsid are reinforced by formation of
intersubunit β-sheets with N-terminal segments of auxiliary protein trimers.
Unexpectedly, the capsid has T=7 quasi-symmetry, despite the P23-45 genome being
twice as large as those of known T=7 phages, in which the DNA is compacted to
near-crystalline density. Our data explain this anomaly, showing how the
canonical HK97 fold has adapted to double the volume of the capsid, while
maintaining its structural integrity. Reconstructions of the procapsid and the
expanded capsid defined the structure of the single vertex containing the portal
protein. Together with a 1.95-Å resolution crystal structure of the portal
protein and DNA packaging assays, these reconstructions indicate that capsid
expansion affects the conformation of the portal protein, while still allowing
DNA to be packaged. These observations suggest a mechanism by which structural
events inside the capsid can be communicated to the outside.
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