Biology Reference
In-Depth Information
Helical structures are formed by multiple copies of coat protein stacked
around a central axis. The nucleic acid binds the protein helix via electrostatic
interactions. The properties of the helical structure can be described by the
number of turns, the number of coat proteins per turn, and the
, meaning
the distance along the helical axis corresponding to exactly one turn (for a
textbook on virus structure and assembly see
pitch
by
Roy, 2005). TMV, for example, is about 300 nm in length, has a diameter of
18 nm, and is formed by 2130 identical coat proteins. These coat proteins
form a closely packed helix with a
Advances in Virus Research
of ca. 2.3 nm with 16 1/3 subunits
per turn. The tube has a hollow cylindrical channel of about 4 nm in diameter
(Namba & Stubbs, 1986) (see also DPV; http://www.dpvweb.net, and the
ICTV; http://www.ncbi.nlm.nih.gov/ICTVdb) (Fig. 2.7). The ends of the rods
can sometimes comprise additional structural proteins; this is the case for
the filamentous particles M13 and SIRV2 (discussed in detail in Section 2.3.3
and 2.3.4).
pitch
Figure 2.7
On the left a view perpendicular to the helix; on the right a view down to the helix axis.
Reproduced with permission from Roy, P. (2005)
Schematic of the structure of the rod-shaped virus
Tobacco mosaic virus.
Advances in Virus Research
, Elsevier
Academic Press.
The structures of viral rods can be short or long, and rigid or flexible. For
example, TMV particles are 300 nm in length and form rigid rods. In contrast,
M13 is nearly 1 µm in length and a highly flexible structure. Indeed, it is so
flexible that its ends can be linked together to generate nanorings (Nam
et
al
., 2004).
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