Genetic analysis of the capsid region of astroviruses

Eight serotypes of human astroviruses (HAstV-1 to HAstV-8) have been described. To date, the entire genomes of HAstV-1 and HAstV-2 as well as the ORF2 sequences of HAstV-1-6 and 8 have been reported. In this study, the ORF2 sequences of seventeen strains of HAstVs originating from different countries were determined, as well as the sequence ORF2 of one porcine astrovirus (PAstV) strain. Afterwards, comparison of the capsid protein precursors encoded by ORF2 of 46 strains of HAstVs, PAstV, and feline astrovirus (FAstV) was carried out. A phylogenetic tree showed eight genogroups of HAstVs that corresponded exactly to the serotypes. HAstV-3 and 7 were the most closely related, whereas HAstVs, FAstV, and PAstV segregated from each other. Compared to a PAstV, a FAstV is closer to HAstVs. Furthermore, the capsid protein precursors were divided into four regions (after amino acid residues 424, 688, and 776, respectively) based on sequence identity. Region I was the most conserved, and FAstV was very close in identity to HAstVs. Two amino acid motifs in region I were predicted to contain the common antigenic epitopes. Region II was relatively variable. Deletions and insertions were characteristic of region III, and region IV was relatively conserved. To our knowledge, this is the first comparative sequence analysis of the capsid protein precursors of eight serotypes of HAstVs as well as two animal astroviruses (FAstV and PAstV).