Proteins encoded by open reading frames 3 and 4 of the genome of Lelystad virus (Arteriviridae) are structural proteins of the virion

Abstract

Four structural proteins of Lelystad virus (Arteriviridae) were recognized by monoclonal antibodies in a Western immunoblotting experiment with purified virus. In addition to the 18-kDa integral membrane protein M and the 15-kDa nucleocapsid protein N, two new structural proteins with molecular masses of 45 to 50 kDa and 31 to 35 kDa, respectively, were detected. Monoclonal antibodies that recognized proteins of 45 to 50 kDa and 31 to 35 kDa immunoprecipitated similar proteins expressed from open reading frames (ORFs) 3 and 4 in baculovirus recombinants, respectively. Therefore, the 45-to 50-kDa protein is encoded by ORF3 and the 31to 35-kDa protein is encoded by ORF4. Peptide-N-glycosidase F digestion of purified virus reduced the 45-to 50-kDa and 31-to 35-kDa proteins to core proteins of 29 and 16 kDa, respectively, which indicates N glycosylation of these proteins in the virion. Monoclonal antibodies specific for the 31-to 35-kDa protein neutralized Lelystad virus, which indicates that at least part of this protein is exposed at the virion surface. We propose that the 45-to 50-kDa and 31-to 35-kDa structural proteins of Lelystad virus be named GP3 and GP4, to reflect their glycosylation and the ORFs from which they are expressed. Antibodies specific for GP3 and GP4 were detected by a Western immunoblotting assay in swine serum after an infection with Lelystad virus.

Innate and adaptive immunity against Porcine Reproductive and Respiratory Syndrome Virus

“…Numerous initial studies proposed that a major neutralizing epitope(s) was located on GP5 Dea, 1997, 1998;Weiland et al, 1999;Yang et al, 2000). Besides the neutralizing epitope on GP5, at least another neutralizing epitope was recognized by a monoclonal antibody on the envelope's GP4 (van Nieuwstadt et al, 1996;Yang et al, 2000) and another on the envelope protein M (Yang et al, 2000). Recently, a single amino acid in the M protein was shown to be necessary for polyclonal swine antibody to mediate broadly neutralizing activity (Trible et al, 2015).…”

The structural biology of PRRSV

“…Some GP3 protein is secreted into the cell medium during PRRSV type 2 infections Mardassi et al, 1998;Wierenga et al, 2002) and it was initially thought not to be a structural protein. However, GP3 was subsequently identified as a minor component in both type 1 and 2 viruses (de Lima et al, 2009;van Nieuwstadt et al, 1996;Wissink et al, 2005). In PRRSV type 2, it was demonstrated by immuno-EM that GP3 is exposed on the viral surface (de Lima et al, 2009).…”

“…The GP4 minor envelope protein ranges in size from 178 (type 2) to 183 (type 1) residues (Meulenberg et al, 1997;van Nieuwstadt et al, 1996). GP4 contains a predicted cleaved signal peptide from residues 1 to 21, and most likely one TM helix at residues 156-177 (161-181 for type 1; Fig.…”

Heterogeneity of porcine reproductive and respiratory syndrome virus: implications for current vaccine efficacy and future vaccine development

“…ORFs 2, 3 and 4 of PRRSV encode virion-associated proteins designated as GP2, GP3 and GP4, respectively (Meulenberg et al, , 1997bMeulenberg and Petersen-den Besten, 1996;Van Nieuwstadt et al, 1996). However, the GP3 protein of a Canadian PRRSV isolate encodes a nonvirion-associated, soluble protein (Mardassi et al, 1998), which is similar to the ORF3 protein encoded by lactate dehydrogenase-elevating virus (LDV) (Faaberg and Plagemann, 1997).…”