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site for astrovirus VPg would be located immediately upstream from
the KGK(N/T)K motif, and that its C-terminal cleavage site might be
found between 92-143 amino acid residues downstream from the N-
terminal cleavage site. However, the actual occurrence of a VPg pro-
tein within this region, as well as its boundaries, is yet to be
experimentally confirmed.
Finally, immunoprecipitation studies on HAstV-4 infected CaCo-
2 cells with an antibody against a synthetic peptide corresponding to
the HVR sequence close to the C-terminus of nsP1a led to the detec-
tion of five proteins in the range of 21-27 kDa, and at least one of
them could be post-translationally modified by phosphorylation on its
serine and/or threonine residues. 47 In addition, after finding proteins
larger than expected in nuclear extracts from recombinant baculovirus-
infected cells expressing amino acids 643-940 of nsP1a, Willcocks
et al . also hypothesized post-translational modifications. 48 Since many
proteins destined for the nucleus are heavily glycosylated, the authors
suggested that nsP1a proteins are modified by glycosylation.
Structural Computational Predictions
Although it is thought that all nonstructural proteins would form the
RNA replication complex and that the transmembrane helices present
on nsP1a would anchor the complex to intracellular membranes, the
functional properties of most of the individual proteins of HAstV
have been poorly characterized. Results obtained after making func-
tional predictions using the 3D-PSSM server for each of the different
HAstV uncharacterized non-structural proteins are shown in Table 1.
The previously identified sequence with homology to a death domain
structure is also included. 28 All matches found, except the protease
and the polymerase motifs, displayed just a moderate degree of cer-
tainty, and the only region that did not display any significant match
corresponded to the N-terminal product, which is rich in transmem-
brane helices. Amino acids 191-353 showed structural homology
to the DNA-protecting protein under starved conditions (DPS pro-
tein), a ferritin homolog that unspecifically binds and protects DNA 55 ;
amino acids 596-739 matched a sarcoplasmic calcium-binding
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