AF331831), VR2332 (GenBank accession no. EF536003) and MLV (GenBank accession no. AF159149) available in GenBank. Only the amino acids different from those in the

consensus sequence are indicated. The black boxed residues indicate the difference AA position sites. B, Hydrophobicity plots of ORF3 generated by the Kyte and Doolittle method using by DNAstar program. Major areas of difference are indicated by arrows. a, GC-2 was a representative of other three isolates because the same plots were shown for GCH-3, HQ-5 and HQ-6. b, LS-4 was a representative of other Fostamatinib chemical structure two isolates because the same plots were shown for LS-4 and ST-7. c, VR2332 was a representative of other two reference virus because the same plots were shown for VR2332, BJ-4 and MLV. The glycoprotein 4 (gp4) is also a minor component of the PRRSV envelope [7] and a typical class I membrane protein [10]. Sequences of ORF4derived from the tested seven isolates showed an evolutionary divergence of 0.095-0.108 with VR2332, MLV and 0.102-0.114 Buparlisib with BJ-4 (Additional file 6). Previous study revealed that the gp4 protein of a North American strain of PRRSV contained one immunodominant domain, comprising amino acid residues 51-65 [33]. In our study, those mutations at AA positions 9(V→L), 32(A→S), 56 (R→G), 59 (A→S), 61 (E→P) and 78(V→I) obviously affect the hydrophobicity of gp4 protein compared to VR2332 and MLV (Figure 4). The core

of a neutralization domain of the glycoprotein encoded by ORF4 of Lelystad virus and recognized by MAbs consists of amino acids 59 to 67 and is located at the most variable region of the protein [35]. The two mutations of positions 59 (A→S) and 61 (E→P) exactly located within this region and may affect the antigenicity

of Chinese isolates in the present study. Antigenic index analysis revealed that seven antigenic changes for virus isolate LS-4, GCH-3, HM-1, HQ-5, HQ-6 and ST-7 and five antigenic changes for virus isolate GC-2 were observed (Additional file 7). However, further studies are necessary to demonstrate whether the putative linear epitope identified in the present study is recognized by neutralizing antibodies. Figure 4 The deduced amino acid sequence comparison and hydrophobicity profiles of the gp4 proteins between the 7 isolates and reference viruses. Deduced amino acid sequence comparison of the gp4 proteins between the 7 isolates from China Baricitinib (GenBank accession no. EU017512, EU177105, EU177110, EU177119, EU177113, EU255926 and EU366150) and another Chinese isolates (BJ-4) (GenBank accession no. AF331831), VR2332 (GenBank accession no. EF536003) and MLV (GenBank accession no. AF159149) available in GenBank. Only the amino acids different from those in the consensus sequence are indicated. The black boxed residues indicate the difference AA position sites. Glycoprotein 5 (gp5) is one of the major structural proteins encoded by PRRSV and forms disulfide-linked heterodimers with M protein in the viral envelope [7].