Biology Reference
In-Depth Information
L2 in HPV Capsids
Although the papillomavirus capsid can be assembled from L1 alone,
the virion always contains L2 as a minor component in the center of
a pentavalent capsomere at the virion vertices.
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It is as yet to be inves-
tigated how L2 and L1 interact with each other in the formation of
the particles.
Zhou
et al
.
20
showed that the amino-terminus of HPV16 L2,
which is located inside the capsid, is able to bind DNA, suggesting a
role for L2 in attracting viral DNA during the assembly of viral parti-
cles. So far the specific nucleotide sequence for efficient binding with
L2 has not been found.
We showed that mouse monoclonal antibodies recognizing epi-
topes within regions of amino acid (aa) 69-81 and aa108-120 of
HPV16 L2 bind to the L1/L2-capsids, indicating that the regions are
located on the surface of the capsid.
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Production of Infectious Pseudovirions
Several methods have been developed to prepare infectious HPV
pseudovirions by encapsidating reporter plasmid DNA into L1/L2-
capsids. The pseudovirions are used in place of HPV virions to study
the functions of the capsid proteins in viral infection and the neutral-
izing activities of anti-HPV antibodies.
Roden
et al
.
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produced HPV16 pseudovirions by packaging
BPV1 DNA in BPHE-1 cells — a hamster fibroblast line harboring
the BPV1 genomic DNA as autonomously replicating episomes, but
not expressing the BPV1 capsid protein genes — by using defective
Semliki Forest virus as an expression vector. Co-expression of HPV16
L1 and L2 in the cells results in production of HPV16 L1/L2-capsids
containing BPV1 genomic DNA. The infectivity can be assayed by
counting the number of foci of transformed cells in the mouse C127
culture infected with the pseudovirions.
Recently, Buck
et al.
23
introduced a system to produce pseudoviri-
ons easily by using the plasmids encoding the codon-modified HPV16
L1 and L2 genes and the cells expressing SV40 T antigen, such as
