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PDBsum entry 1vak
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References listed in PDB file
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Key reference
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Title
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T=1 capsid structures of sesbania mosaic virus coat protein mutants: determinants of t=3 and t=1 capsid assembly.
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Authors
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V.Sangita,
G.L.Lokesh,
P.S.Satheshkumar,
C.S.Vijay,
V.Saravanan,
H.S.Savithri,
M.R.Murthy.
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Ref.
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J Mol Biol, 2004,
342,
987-999.
[DOI no: ]
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PubMed id
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Abstract
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Sesbania mosaic virus particles consist of 180 coat protein subunits of 29kDa
organized on a T=3 icosahedral lattice. N-terminal deletion mutants of coat
protein that lack 36 (CP-NDelta36) and 65 (CP-NDelta65) residues from the N
terminus, when expressed in Escherichia coli, produced similar T=1 capsids of
approximate diameter 20nm. In contrast to the wild-type particles, these contain
only 60 copies of the truncated protein subunits (T=1). CP-NDelta65 lacks the
"beta-annulus" believed to be responsible for the error-free assembly
of T=3 particles. Though the CP-NDelta36 mutant has the beta-annulus segment, it
does not form a T=3 capsid, presumably because it lacks an arginine-rich motif
found close to the amino terminus. Both CP-NDelta36 and CP-NDelta65 T=1 capsids
retain many key features of the T=3 quaternary structure. Calcium binding
geometries at the coat protein interfaces in these two particles are also nearly
identical. When the conserved aspartate residues that coordinate the calcium,
D146 and D149 in the CP-NDelta65, were mutated to asparagine
(CP-NDelta65-D146N-D149N), the subunits assembled into T=1 particles but failed
to bind calcium ions. The structure of this mutant revealed particles that were
slightly expanded. The analysis of the structures of these mutant capsids
suggests that although calcium binding contributes substantially to the
stability of T=1 particles, it is not mandatory for their assembly. In contrast,
the presence of a large fraction of the amino-terminal arm including sequences
that precede the beta-annulus and the conserved D149 appear to be indispensable
for the error-free assembly of T=3 particles.
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Figure 6.
Figure 6. Stereo view of calcium binding region in CP-ND65
(red) and the corresponding region in CP-ND65-D146N-D149N
(blue). D146 and D149, which participate in calcium coordination
in CP-ND65, have undergone changes in CP-ND65-D146N-D149N. The
C-terminal residues, which also coordinate to calcium in
CP-ND65, are disordered in CP-ND65-D146N-D149N and, hence, are
not shown.
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Figure 8.
Figure 8. Schematic illustration of the effects of deleting
segments corresponding to the N-ARM and the b-annulus and
mutations of residues contributing ligands to calcium on
particle assembly. Space filling models of T=3 (native), T=1
(CP-ND65) and swollen T=1 (CP-ND65-D146N-D149N) capsids were
generated using the refined coordinates of the subunits in the
respective structures.
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The above figures are
reprinted
by permission from Elsevier:
J Mol Biol
(2004,
342,
987-999)
copyright 2004.
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