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Comparative Study
. 2013 Feb 5;436(1):8-14.
doi: 10.1016/j.virol.2012.09.040. Epub 2012 Oct 16.

Comparison of novel MLB-clade, VA-clade and classic human astroviruses highlights constrained evolution of the classic human astrovirus nonstructural genes

Hongbing Jiang  1 , Lori R Holtz, Irma Bauer, Carl J Franz, Guoyan Zhao, Ladaporn Bodhidatta, Sanjaya K Shrestha, Gagandeep Kang, David Wang
Affiliations
Comparative Study

Comparison of novel MLB-clade, VA-clade and classic human astroviruses highlights constrained evolution of the classic human astrovirus nonstructural genes

Hongbing Jiang et al. Virology. .

Abstract

Eight serotypes of human astroviruses (the classic human astroviruses) are causative agents of diarrhea. Recently, five additional astroviruses belonging to two distinct clades have been described in human stool, including astroviruses MLB1, MLB2, VA1, VA2 and VA3. We report the discovery in human stool of two novel astroviruses, astroviruses MLB3 and VA4. The complete genomes of these two viruses and the previously described astroviruses VA2 and VA3 were sequenced, affording seven complete genomes from the MLB and VA clades for comparative analysis to the classic human astroviruses. Comparison of the genetic distance, number of synonymous mutations per synonymous site (dS), number of non-synonymous mutations per non-synonymous site (dN) and the dN/dS ratio in the protease, polymerase and capsid of the classic human, MLB and VA clades suggests that the protease and polymerase of the classic human astroviruses are under distinct selective pressure.

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Figures

FIG. 1
FIG. 1
Phylogenetic analysis of the astrovirus open reading frames. Phylogenetic trees were generated by the maximum likelihood method with 1000 replicates based on amino acids alignments. Significant bootstrap values (>700) are shown. (A) ORF1a serine proteinase. (B) ORF1b RNA dependent RNA polymerase (RdRp). (C) ORF2 capsid protein. Scale bars represent the number of differences in each ORF.
FIG. 2
FIG. 2
Conserved motifs in the 5′ UTR of MLB clade astroviruses and the 3′ UTR of VA clade astroviruses. (A) Multiple sequence alignment of the 30 nt at the very 5′ end of each MLB clade astrovirus genome. (B) 150 nt from the 3′ terminus of each of the VA clade astroviruses were aligned. The portion of the alignment containing a perfectly conserved 33 nt stretch is shown.
FIG. 3
FIG. 3
Pairwise genetic p-distance comparisons for MLB, VA, avian and classic human astroviruses. TAstV: turkey astrovirus, HAstV: human astrovirus. TABLE 1: Epidemiological data
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