Biology Reference
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spacing for HCMV was 23 Å, indicating that the larger HCMV
genome is more closely packed than that of HSV-1.
KSHV Capsid
Gammaherpesvirus structures are not as well studied as alpha- and
betaherpesvirus structures due to difficulties in viral culturing and
isolation of either EBV or KSHV. Wu
et al
. obtained the first cap-
sid structure of a gammaherpesvirus, KSHV, in 2000 (Fig. 6f ).
78
In these studies, KSHV in lymphoma cell cultures was induced to
lytic replication using 12-
O
-tetradecanoylphorbol-13-acetate, yield-
ing sufficient quantities of virus capsids for cryoEM studies. The
24 Å 3D structure of the KSHV capsid has the same T
16 icosa-
hedral symmetry as that of HSV-1 and HCMV capsids and has the
same organization of 12 pentons, 150 hexons and 320 triplexes. The
existence of KSHV A, B, and C capsids, similar to those of HSV-1,
was further demonstrated subsequently.
79,80
These studies showed
that the gross morphology of the capsid is highly conserved among
herpesviruses, although the pentons, hexons, and triplexes differ
slightly in shape.
80,81
Despite success in pushing the resolution of the HSV-1 capsid
beyond subnanometer resolution,
34
similar efforts for human beta-
and gammaherpesviruses have met with difficulties. The purification
process for HCMV and KSHV is still relatively low yield. Future
assembly and structural studies of beta- and gammaherpesviruses
toward higher resolution may depend on non-human viruses such as
simian cytomegalovirus,
82
rhesus monkey rhadinovirus,
83
and murine
gammaherpesvirus-68 (MHV-68).
59
These non-human pathogens
replicate to high titer in culture, and their capsid, tegument, and
envelope proteins share homology with those of HCMV (in the case
of simian cytomegalovirus) and KSHV or EBV (in the case of rhesus
monkey rhadinovirus and MHV-68). A recent study examined rhesus
monkey rhadinovirus A, B, and C capsids in an attempt to understand
gammaherpesvirus capsid maturation and DNA packaging.
83
=
