Biology Reference
In-Depth Information
VP1: P2 Subdomain
The P2 subdomain has been described as a large insertion, distal
globular portion of the arch, and a replaceable module. Amino acid
alignments have shown that the P2 subdomain is the most variable
region. In addition, a large number of insertions were seen in two
genera, Sapovirus and Vesiviruis , with respect to Norovirus . The P2
subdomain occupies the residues 279 to 405 of NoV VP1. The P2
residues 285 to 380 fold into a compact barrel-like structure con-
sisting of six
strands. 28 The fold of this subdomain was found to be
similar to the elongation factor-Tu (EF-Tu). The EF-Tu is a GTP
binding protein involved in transporting aminoactyl-tRNAs to ribo-
somes, which suggests a possible role in viral or cellular RNA trans-
lation and regulation of protein synthesis. In addition, the P2
subdomain is thought to contain the determinants of strain speci-
ficity, cell binding, and antigencity. For example, monoclonal anti-
bodies that recognize regions in the P2 subdomain inhibit binding
of NoV VLPs to cells. 33,34
β
Subunits
In order for NoV to form a T
3 icosahedral structure, the capsid
protein forms three quasiequivalent positions, termed A, B, and C. 28
The structures of the A and B subunits are similar, maintaining rela-
tive orientations between the S and P domains. The S domain is
involved in the icosahedral contacts, whereas the P domain is
involved in the dimeric contacts. The dimers on the local twofolds
axes are formed by A and B subunits, whereas those on the strict axes
are formed by two C subunits. These three subunits form dimers,
denoted AB and CC. The S domains of the AB dimer have a “bent”
confirmation, whereas the S domains of the CC dimer have a “flat”
confirmation. These confirmations allow for the formation of a
closed shell. The AB dimers surround the icosahedral fivefolds axes,
whereas the AB and CC dimers alternate around the icosahedral
threefold axes.
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