Biology Reference
In-Depth Information
the amino acid residues in the bottom region, which interact with the
surface of the core particle, as described above. Furthermore, the elec-
trostatic potential at the edge of P8-trimers of RGDV, which might
similarly play an important role in the interactions between P8-trimers
in RDV,
2
revealed obvious patches of positive and negative charge,
which would allow clear electrostatic complementarity among adja-
cent subunits (Fig. 8, side view). This electrostatic complementarity
would allow a second outer layer to form with a different and heterol-
ogous viral protein
22
because of similar amino acid sequences and
electrostatic similarities, in spite of the fact that the homology at the
amino acid level between the heterologous P8 proteins from RDV
and RGDV is only 52%. Thus, binding of neighboring P8-trimers to
the T-trimer via the mutual binding of P8-trimers allowed P8 to poly-
merize and cover the total surface of the core particle in a mismatched
manner, with a T
13
l
structure.
When sitting of P8-trimers on the P3 core capsid proteins was
analyzed, it was clear that all the junctions formed by the organization
of P3 protein monomers were covered by P8-trimers (Figs. 1 and 6).
Thus, it seems likely that the role of the T
=
13
l
structure of the sec-
ond and outer layer, found in the viruses that belong to
Reoviridae
,
might be to protect the interior portion of the virus from attack by the
agents in the host cell's cytoplasm, such as ions and free radicals, for
example. If this is the case, the mismatches in the T
=
13
l
structure, in
which P8-trimers bind at environmentally different sites on the inner
surface of the capsid, provide a structure that, while hard to under-
stand from a biochemical perspective, apparently represents a sophis-
ticated defense by the virus against, for example, attack by its host.
=
The Rigid Structural Unit of the Outer Capsid,
the P8-trimer
Unlike the first-layer capsid protein P3, which is thin and flat, the
P8-trimer, which is the subunit that forms the second layer, appears to
be granular in shape. When P8 proteins form trimers, each P8 protein
wraps around another in a right-handed manner and subunits “swap”
