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Molecular Dissection of the Forces Responsible for Viral Capsid Assembly and Stabilization by Decoration Proteins
journal contribution
posted on 2016-12-28, 00:00 authored by Shannon Lambert, Qin Yang, Rolando De Angeles, Jenny R. Chang, Marcos Ortega, Christal Davis, Carlos Enrique CatalanoComplex double-stranded
DNA viruses utilize a terminase enzyme
to package their genomes into a preassembled procapsid shell. DNA
packaging triggers a major conformational change in the proteins assembled
into the shell and most often subsequent addition of a decoration
protein that is required to stabilize the structure. In bacteriophage
λ, DNA packaging drives a procapsid expansion transition to
afford a larger but fragile shell. The gpD decoration protein adds
to the expanded shell as trimeric spikes at each of the 140 three-fold
axes. The spikes provide mechanical strength to the shell such that
it can withstand the tremendous internal forces generated by the packaged
DNA in addition to environmental insults. Hydrophobic, electrostatic,
and aromatic–proline noncovalent interactions have been proposed
to mediate gpD trimer spike assembly at the expanded shell surface.
Here, we directly examine each of these interactions and demonstrate
that hydrophobic interactions play the dominant role. In the course
of this study, we unexpectedly found that Trp308 in the λ major
capsid protein (gpE) plays a critical role in shell assembly. The
gpE-W308A mutation affords a soluble, natively folded protein that
does not further assemble into a procapsid shell, despite the fact
that it retains binding interactions with the scaffolding protein,
the shell assembly chaparone protein. The data support a model in
which the λ procapsid shell assembles via cooperative interaction
of monomeric capsid proteins, as observed in the herpesviruses and
phages such as P22. The significance of the results with respect to
capsid assembly, maturation, and stability is discussed.
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Decoration Proteins Complex double-stranded DNA virusesshell assembly chaparone proteinshell surfaceλ procapsid shellgpD decoration proteincapsid assemblyprocapsid expansion transitionpreassembled procapsid shellMolecular Dissectionscaffolding proteincapsid proteingpE-W 308A mutationgpD trimer spike assemblytrimeric spikesterminase enzymedata supportmonomeric capsid proteinsDNA packaging triggersprocapsid shellP 22.binding interactionsViral Capsid Assemblydecoration proteinTrp 308shell assembly
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