Identification and characterization of a novel structural glycoprotein in pseudorabies virus, gL

B G Klupp, J Baumeister, A Karger, N Visser, T C Mettenleiter
1994 Journal of Virology  
Herpesvirus envelope glycoproteins play important roles in the interaction between virions and target cells. In the alphaherpesvirus pseudorabies virus (PrV), seven glycoproteins that all constitute homologs of glycoproteins found in herpes simplex virus type 1 (HSV-1) have been characterized, including a homolog of HSV-1 glycoprotein H (gH). Since HSV-1 gH is found associated with another essential glycoprotein, gL, we analyzed whether PrV also encodes a gL homolog. DNA sequence analysis of a
more » ... ence analysis of a corresponding part of the UL region adjacent to the internal inverted repeat in PrV strains Kaplan and Becker revealed the presence of two open reading frames (ORF). Deduced proteins exhibited homology to uracil-DNA glycosylase encoded by HSV-1 ORF UL2 (54% identity) and gL encoded by HSV-1 ORF ULl (24% identity), respectively. To identify the PrV ULl protein, rabbit antisera were prepared against two synthetic oligopeptides that were predicted by computer analysis to encompass antigenic epitopes. Sera against both peptides reacted in Western blots of purified virions with a 20-kDa protein. The specificity of the reaction was demonstrated by peptide competition. Since the PrV ULl sequence did not reveal the presence of a consensus N-linked glycosylation site, concanavalin A affinity chromatography and enzymatic deglycosylation of virion glycoproteins were used to ascertain that the PrV ULl product is 0 glycosylated. Therefore, we designated this protein PrV gL. Analysis of mutant PrV virions lacking gH showed that concomitantly with the absence of gH, gL was also missing in purified virions. In summary, we identified and characterized a novel structural PrV glycoprotein, gL, which represents the eighth PrV glycoprotein described. In addition, we show that virion location of PrV gL is dependent on the presence of PrV gH. Herpesvirions consist of a nucleocapsid containing the double-stranded linear DNA genome, which is surrounded by an amorphous tegument structure and the virion envelope. In this outer membrane, virus-encoded glycoproteins are embedded. These structural glycoproteins play important roles in the interaction between herpesviruses and their hosts both in mediating infection of target cells and in eliciting immune responses. Among the alphaherpesviruses, herpes simplex virus type 1 (HSV-1) has been shown to encode at least 11 glycoproteins, designated gB through gE and gG through gM (2, 62). Four of these glycoproteins (gB, gD, gH, and gL) are essential. Pseudorabies virus (PrV), the causative agent of Aujeszky's disease in pigs, is also a member of the Alphaherpesvirinae. Its envelope contains at least six glycoproteins, designated gB (gll), gC (glll), gD (gpSO), gE (gI), gI (gp63), and gH (29, 37, 42, 44) , that all exhibit homology to respective glycoproteins in HSV-1. Glycoprotein B homologs represent the most highly conserved group of herpesvirus glycoproteins; the second most highly conserved group are the gH homologs. Both gB and gH have been found in members of all three subfamilies of herpesviruses (1, 10, 15, 43, 64), which implies an important role for these molecules in the life cycle of the respective virus. Glycoprotein B homologs are essential for virus penetration and cell-to-cell spread (6, 46, 51, 55, 56) . The gH proteins have also been found to be required for penetration and cell-to-cell spread (19, 22, 26, 28, 47, 50) , and antibodies against several gH homologs possess potent com-* Corresponding author. Mailing address:
doi:10.1128/jvi.68.6.3868-3878.1994 fatcat:lgwerpuha5dlfjfiwd7mnq4wqm