Biology Reference
In-Depth Information
acids of P3 are important for the stabilization of CLPs at high concen-
trations of MgCl
2
. The theoretical interactions between two molecules
of P3 in an asymmetric dimer include 11 strong hydrogen bonds and
four strong salt bridges within this amino-terminal arm among the 19
strong hydrogen bonds and 12 strong salt bridges involved in the entire
interaction between P3s.
7
Thus, the stability of P3A-P3B interactions
fell gradually with increased deletion of amino-terminal residues. These
results suggest that the reduction in stability of the CLPs obtained with
the amino-terminally deleted mutant P3 proteins was caused by loss of
the bonds described above.
Calculations of the total energy of interaction for asymmetric
dimers in reoviruses, based on their atomic structure, indicated that
asymmetric P3 dimers of RDV have a higher energy of interaction
(207.3 kcal/mol) than those of VP3 of BTV (134.1 kcal/mol), and
the amino-terminal region seems to be responsible for this difference.
In the case of N52del-P3 of RDV, which had lost the capacity for
self-assembly, the total energy of the P3A-P3B interaction was less
than half (92.2 kcal/mol) of that of the native P3-P3 interaction. The
relatively high energy of interaction between P3 monomers in P3
dimers in RDV, due to the amino-terminal region of P3, probably
allows cores of RDV to form in the absence of other structural pro-
teins. The requirement for an additional protein (VP7) in BTV
10,11
for
the construction of CLPs might be due to the lower energy of the
interaction between the monomers that correspond to P3 in BTV. In
orthoreovirus, the formation of inner core particles by mutant core-
capsid protein
1 — from which the amino-terminal 230 amino acids
of the wild type have been removed (N230del-ramda1; 99.5 kcal/
mol) — might be due to assistance by the
λ
2 protein.
12
Inside the first-layer capsid of RDV there is a 25.7 kbp dsRNA with
12 segments.
13
To our knowledge, this genome is the largest among
those of dsRNA viruses studied by X-ray crystallography to date. The
cavity also contains P1, a putative RNA-dependent RNA polymerase; P5,
a putative guanylyltransferase; and P7, a non-specific nucleic acid-binding
protein. It seems reasonable that a large cavity should be required to
enclose both dsRNA and the molecules involved in transcription. The
generation of strongly interacting dimers that allow the side-by-side
binding of the very thin P3 proteins
2
allows creation of this large cavity.
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