The bovine herpesvirus type 1 UL3.5 open reading frame encodes a virion structural protein

Protein Composition of the Bovine Herpesvirus 1.1 Virion

Bovine herpesvirus (BoHV) type 1 is an important agricultural pathogen that infects cattle and other ruminants worldwide. Acute infection of the oro-respiratory tract leads to immune suppression and allows commensal bacteria to infect an otherwise healthy lower respiratory tract. This condition is known as the Bovine Respiratory Disease (BRD). BoHV-1 latently infects the host for life and periodical stress events re-initiate BRD, translating into high morbidity and large economic losses. To gain a better understanding of the biology of BoHV-1 and the disease it causes, we elucidated the protein composition of extracellular virions using liquid chromatography-mass spectrometry analysis. We detected 33 viral proteins, including the expected proteins of the nucleocapsid and envelope as well as other regulatory proteins present in the viral tegument. In addition to viral proteins, we have also identified packaged proteins of host origin. This constitutes the first proteomic characterization of the BoHV virion.

Equine herpesvirus type 1 (EHV-1) open reading frame 59 encodes an early protein that is localized to the cytosol and required for efficient virus growth

Equine herpesvirus type 1 (EHV-1) ORF59 is predicted to encode a protein consisting of 180 amino acids. To determine whether ORF59 in fact encodes a protein, sequences encoding an HA epitope (YPYDVPDYA) was inserted at the carboxyterminus of the ORF59 protein in EHV-1 strain Ab4. Using anti-HA monoclonal antibodies, a 21-kDa band was specifically detected by western blot analysis in lysates of cells infected with a recombinant EHV-1 from strain Ab4 that carries the pORF59-HA but not in cells infected with parental Ab4. Further characterization of the protein using immunofluorescence and fractionation studies showed that pORF59 is an early protein that localizes to the cytosol in virus-infected cells. Recombinant EHV-1 lacking ORF59 (rAb4∆59) exhibited a small-plaque phenotype and could not be propagated. Our findings suggest that the ORF59 protein plays a major role in EHV-1 replication in vitro and likely in vivo.

Relevance of the interaction between alphaherpesvirus UL3.5 and UL48 proteins for virion maturation and neuroinvasion

The UL3.5 and UL48 genes, which are conserved in most alphaherpesvirus genomes, are important for maturation of pseudorabies virus (PrV) particles in the cytoplasm of infected cells (W. Fuchs, B. G. Klupp, H. J. Rziha, and T. C. Mettenleiter, J. Virol. 70:3517-3527, 1996; W. Fuchs, H. Granzow, B. G. Klupp, M. Kopp and T. C. Mettenleiter, J. Virol. 76:6729-6742, 2002). In bovine herpesvirus 1 (BoHV-1), the homologous gene products pUL3.5 and pUL48 have been demonstrated to interact physically (N. Lam and G. Letchworth, J. Virol. 74:2876-2884, 2000). Moreover, BoHV-1 pUL3.5 partially complemented a pUL3.5 defect in PrV (W. Fuchs, H. Granzow, and T. C. Mettenleiter, J. Virol. 71:8886-8892, 1997). By using coimmunoprecipitation and yeast two-hybrid studies, we observed a similar interaction between pUL3.5 and pUL48 of PrV, as well as a heterologous interaction between the PrV and BoHV-1 gene products. The relevant domain could be confined to the first 43 amino acids of PrV pUL3.5. Unlike its BoHV-1 homologue, PrV pUL3.5 is processed by proteolytic cleavage, and only an abundant 14-kDa fragment consisting of amino acids 1 to >or=116 could be detected by peptide mass fingerprint analysis of purified wild-type PrV particles, which also contain the pUL48 tegument component. To determine the biological relevance of the protein-protein interaction, pUL3.5-, pUL48-, and double-negative PrV mutants were analyzed in parallel. All deletion mutants were replication competent but exhibited significantly reduced plaque sizes and virus titers in cultured rabbit kidney cells compared to wild-type and rescued viruses, which correlated with a delayed neuroinvasion in intranasally infected mice. Remarkably, the defects of the double-negative mutant were similar to those of pUL48-negative virus. Electron microscopy of cells infected with either deletion mutant revealed the retention of naked nucleocapsids in the cytoplasm and the absence of mature virus particles. In summary, our studies for the first time demonstrate the relevance of the pUL3.5-pUL48 interaction for secondary envelopment of an alphaherpesvirus, give a molecular basis for the observed trans-complementation between the PrV and BHV-1 pUL3.5 homologs, yield conclusive evidence for the incorporation of a proteolytically processed pUL3.5 into PrV virions, and demonstrate the importance of both proteins for neuroinvasion and neurovirulence of PrV.

Bovine herpesvirus 1 U(L)3.5 interacts with bovine herpesvirus 1 alpha-transinducing factor

The bovine herpesvirus 1 (BHV-1) U(L)3.5 gene encodes a 126-amino-acid tegument protein. Homologs of U(L)3.5 are present in some alphaherpesviruses and have 20 to 30% overall amino acid homology that is concentrated in the N-terminal 50 amino acids. Mutant pseudorabies virus lacking U(L)3.5 is deficient in viral egress but can be complemented by BHV-1 U(L)3.5 (W. Fuchs, H. Granzow, and T. C. Mettenleiter, J. Virol. 71:8886-8892, 1997). The function of BHV-1 U(L)3.5 in BHV-1 replication is not known. To get a better understanding of its function, we sought to identify the proteins that interact with the BHV-1 U(L)3.5 protein. By using an in vitro pull-down assay and matrix-assisted laser desorption ionization mass spectrometry analysis, we identified BHV-1 alpha-transinducing factor (alphaBTIF) as a BHV-1 U(L)3. 5-interacting protein. The interaction was verified by coimmunoprecipitation from virus-infected cells using an antibody to either protein, by indirect immunofluorescence colocalization in both virus-infected and transfected cells, and by the binding of in vitro-translated proteins. In virus-infected cells, U(L)3.5 and alphaBTIF colocalized in a Golgi-like subcellular compartment late in infection. In transfected cells, they colocalized in the nucleus. Deletion of 20 amino acids from the N terminus of U(L)3.5, but not 40 amino acids from the C terminus, abolished the U(L)3.5-alphaBTIF interaction both in vitro and in vivo. The interaction between U(L)3. 5 and alphaBTIF may be important for BHV-1 maturation and regulation of alphaBTIF transactivation activity.

Varicella-zoster virus ORF57, unlike its pseudorabies virus UL3.5 homolog, is dispensable for viral replication in cell culture

Varicella zoster virus (VZV) encodes five genes that do not have homologs in herpes simplex virus. One of these genes, VZV ORF57, is predicted to encode a protein containing 71 amino acids. Antibody to ORF57 protein immunoprecipitated a 6-kDa protein in the cytosol of VZV-infected cells. Although the homolog of VZV ORF57 in pseudorabies virus, UL3.5, is critical for viral egress and growth in cell culture, VZV unable to express ORF57 replicated to titers similar to those seen with parental virus. Thus VZV ORF57 has a different role in viral replication than its pseudorabies virus homolog.