Biology Reference
In-Depth Information
Fig. 3.
Structure of the MS2 coat protein dimer. View from inside (left)
and outside (right) the virus particle. One monomer is shown in red and
orange, the other one in blue and cyan (1MSC).
-meander topology (Fig. 3). The fundamental building block of
the viral protein shell is the compact protein dimer that exists in two
distinct but similar conformations. In the dimer 10 of the
in a
β
β
-strands
form a twisted
-sheet that points toward the interior of the virus and
thus the RNA, whereas the
β
-helices are on the surface of the parti-
cle (Fig. 3).
5,12
The surface of the
α
-sheet has an excess of positively
charged amino acids, resulting in an overall positive electrostatic envi-
ronment ideal for interactions with the poly-anionic RNA.
β
The RNA-Coat Protein Complex
The structure of the complex between the MS2 coat protein and
the packaging signal RNA hairpin has been extensively studied by X-
crystallography
4,5,12-16
and biochemical approaches.
2,17-20
In the virus
-sheet of the protein dimer faces toward the RNA-
filled interior of the particle. The RNA hairpin binds to this sheet
and contacts both subunits of the dimer (Fig. 4). The helical axis of
the short stem is oriented almost parallel to the strands of the sheet.
The 5´ side of the stem and part of the loop are facing the protein. The
total interaction surface between RNA and protein is approximately
1700 Å
2
. Twenty-one amino-acid residues in the dimer are directly
involved in interactions with the RNA (Fig. 4). Of these, 13 contact
the bases of nucleotides
the 10-stranded
β
−
4,
−
5, and
−
10, which have been shown to
