Comparative analysis of the open reading frames protein genes of genotype 4 Hepatitis E virus in swine and wild boar

Abstract

The goal of this study was to determine the molecular diversity of the open reading frames (ORFs) ORF1, ORF2, ORF3 protein genes from full-length genomes of genotype 4 hepatitis E virus (HEV) from pigs and wild boars at protein and gene level. Statistical technique Shannon entropy was used for mutational analysis of ORF1–ORF3 protein genes to identify amino acid substitutions in the HEV 4 sequences isolated from pigs and wild boars that were most susceptible to mutations. Gene selective pressure for genes was estimated using Tajima’s neutrality test. The ORF regions of 11 swine and 11 wild boar genotype 4 HEV isolates with complete genomes from the GenBank database were analyzed comparatively. The total number of polymorphic sites was determined. Nonsynonymous (amino acid changing) and synonymous (amino acid preserving) substitutions were identified in ORF1, ORF2, ORF3 in swine and wild boar HEV 4 isolates. No evidence of recombination was found for ORFs in 11 swine HEV 4 isolates, ORF2, ORF3 in 8 wild boar HEV 4 isolates. However, a recombination fragment with a length of 430 nucleotides was detected in the ORF1 gene of 3 wild boar HEV 4 isolates. Positive D Tajima factors were determined for ORF1, ORF2, ORF3 genes of swine HEV 4 and ORF1, ORF2 genes of wild boar HEV 4. While a negative value of D Tajima’s factor was determined for ORF3 gene of wild boar HEV 4. Molecular characteristics showing principal distinctions between the open-reading frames of swine and wild boar genotype 4 hepatitis E virus were obtained. Wild boar ORF1 is characterized by lower nucleotide diversity π value (0.144) and higher number of segregated sites S value (1,688) comparing with higher π value (0.159) and lower S value (1,602) of swine ORF1. Positive values of D Tajima’s factor for ORF1, ORF2 ORF3 genes of swine HEV 4 and ORF1, ORF2 genes of wild boar HEV 4 show on positive selection of these genes. Negative value of D Tajima’s factor for ORF3 gene of wild boar HEV 4 indicates onto purifying selection decreasing variability in ORF3 gene of wild boar HEV 4. The largest number of amino acid variation sites (19.2%) was found for wild boar HEV 4 ORF3 followed by swine HEV 4 ORF3 (15.7%) comparing with other swine and wild boars HEV 4 ORFs