Identification of a hydrophobic domain of HA2 essential to morphogenesis of Helicoverpa armigera nucleopolyhedrovirus

Amino acid substitutions Q129N and T131N/M133T in hepatitis B surface antigen (HBsAg) interfere with the immunogenicity of the corresponding HBsAg or viral replication ability

Variants of hepatitis B surface antigen (HBsAg) influenced its antigenicity and immunogenicity. In our study, we aim to investigate biological significance of amino acid (aa) substitutions in HBsAg, Q129 N and T131 N/M133 T, for glycosylation, antigenicity and immunogenicity of variant HBsAg (vtHBsAg) and viral replication. Expression plasmids of vtHBsAg with aa substitutions Q129 L, T123 N, Q129 N and T131 N/M133 T were constructed. Immunofluorescence (IF) staining and Western blot were simultaneously utilized to examine expression of vtHBsAg proteins in Huh7 cells transfected with vtHBsAg constructs. vtHBsAg of Q129 N and T131 N/M133 T created new N-glycosylation and displayed perinuclear distribution by IF staining with the anti-HA. Antigenicity of vtHBsAg of Q129 N and T131 N/M133 T was reduced compared with wild type (wt) HBsAg. In addition, we discovered impaired ability to induce anti-HBs responses against wtHBsAg in mice immunized with plasmids pHBsAg- Q129 N and T131 N/M133 T. Even so, efficient protective response toward wild type HBV can be primed by the two vtHBsAgs in mice. Further, we discovered that vtHBsAg with Q129 N distinctly impaired HBV replication capacity, but vtHBsAg with T131 N/M133 T had no impact on viral replication. Thus, we conclude that vtHBsAg with Q129 N or T131 N/M133 T creates new N-glycosylation and interferes with both the antigenicity and immunogenicity of vtHBsAg. And vtHBsAg with Q129 N impaired HBV replication ability.

Autographa californica Multiple Nucleopolyhedrovirus Ac34 Protein Retains Cellular Actin-Related Protein 2/3 Complex in the Nucleus by Subversion of CRM1-Dependent Nuclear Export

Actin, nucleation-promoting factors (NPFs), and the actin-related protein 2/3 complex (Arp2/3) are key elements of the cellular actin polymerization machinery. With nuclear actin polymerization implicated in ever-expanding biological processes and the discovery of the nuclear import mechanisms of actin and NPFs, determining Arp2/3 nucleo-cytoplasmic shuttling mechanism is important for understanding the function of nuclear actin. A unique feature of alphabaculovirus infection of insect cells is the robust nuclear accumulation of Arp2/3, which induces actin polymerization in the nucleus to assist in virus replication. We found that Ac34, a viral late gene product encoded by the alphabaculovirus Autographa californica multiple nucleopolyhedrovirus (AcMNPV), is involved in Arp2/3 nuclear accumulation during virus infection. Further assays revealed that the subcellular distribution of Arp2/3 under steady-state conditions is controlled by chromosomal maintenance 1 (CRM1)-dependent nuclear export. Upon AcMNPV infection, Ac34 inhibits CRM1 pathway and leads to Arp2/3 retention in the nucleus.

Proteomic Analysis of Mamestra Brassicae Nucleopolyhedrovirus Progeny Virions from Two Different Hosts

Mamestra brassicae nucleopolyhedrovirus (MabrNPV) has a wide host range replication in more than one insect species. In this study, a sequenced MabrNPV strain, MabrNPV-CTa, was used to perform proteomic analysis of both BVs and ODVs derived from two infected hosts: Helicoverpa armigera and Spodoptera exigua. A total of 82 and 39 viral proteins were identified in ODVs and BVs, respectively. And totally, 23 and 76 host proteins were identified as virion-associated with ODVs and BVs, respectively. The host proteins incorporated into the virus particles were mainly involved in cytoskeleton, signaling, vesicle trafficking, chaperone and metabolic systems. Some host proteins, such as actin, cyclophilin A and heat shock protein 70 would be important for viral replication. Several host proteins involved in immune response were also identified in BV, and a C-type lectin protein was firstly found to be associated with BV and its family members have been demonstrated to be involved in entry process of other viruses. This study facilitated the annotation of baculovirus genome, and would help us to understand baculovirus virion structure. Furthermore, the identification of host proteins associated with virions produced in vivo would facilitate investigations on the involvement of intriguing host proteins in virus replication.

Putative phosphorylation sites on WCA domain of HA2 is essential for Helicoverpa armigera single nucleopolyhedrovirus replication

Protein phosphorylation is one of the most common post-translational modification processes that play an essential role in regulating protein functionality. The Helicoverpa armigera single nucleopolyhedrovirus (HearNPV) orf2-encoded nucleocapsid protein HA2 participates in orchestration of virus-induced actin polymerization through its WCA domain, in which phosphorylation status are supposed to be critical in respect to actin polymerization. In the present study, two putative phosphorylation sites ((232)Thr and (250)Ser) and a highly conserved Serine ((245)Ser) on the WCA domain of HA2 were mutated, and their phenotypes were characterized by reintroducing the mutated HA2 into the HearNPV genome. Viral infectivity assays demonstrated that only the recombinant HearNPV bearing HA2 mutation at (245)Ser can produce infectious virions, both (232)Thr and (250)Ser mutations were lethal to the virus. However, actin polymerization assay demonstrated that all the three viruses bearing HA2 mutations were still capable of initiating actin polymerization in the host nucleus, which indicated the putative phosphorylation sites on HA2 may contribute to HearNPV replication through another unidentified pathway.

Proteomics of the Autographa californica nucleopolyhedrovirus budded virions

Baculoviruses produce two progeny phenotypes during their replication cycles. The occlusion-derived virus (ODV) is responsible for initiating primary infection in the larval midgut, and the budded virus (BV) phenotype is responsible for the secondary infection. The proteomics of several baculovirus ODVs have been revealed, but so far, no extensive analysis of BV-associated proteins has been conducted. In this study, the protein composition of the BV of Autographa californica nucleopolyhedrovirus (AcMNPV), the type species of baculoviruses, was analyzed by various mass spectrometry (MS) techniques, including liquid chromatography-triple quadrupole linear ion trap (LC-Qtrap), liquid chromatography-quadrupole time of flight (LC-Q-TOF), and matrix-assisted laser desorption ionization-time of flight (MALDI-TOF). SDS-PAGE and MALDI-TOF analyses showed that the three most abundant proteins of the AcMNPV BV were GP64, VP39, and P6.9. A total of 34 viral proteins associated with the AcMNPV BV were identified by the indicated methods. Thirteen of these proteins, PP31, AC58/59, AC66, IAP-2, AC73, AC74, AC114, AC124, chitinase, polyhedron envelope protein (PEP), AC132, ODV-E18, and ODV-E56, were identified for the first time to be BV-associated proteins. Western blot analyses showed that ODV-E18 and ODV-E25, which were previously thought to be ODV-specific proteins, were also present in the envelop fraction of BV. In addition, 11 cellular proteins were found to be associated with the AcMNPV BV by both LC-Qtrap and LC-Q-TOF analyses. Interestingly, seven of these proteins were also identified in other enveloped viruses, suggesting that many enveloped viruses may commonly utilize certain conserved cellular pathways.

Biological significance of amino acid substitutions in hepatitis B surface antigen (HBsAg) for glycosylation, secretion, antigenicity and immunogenicity of HBsAg and hepatitis B virus replication

Amino acid substitutions of hepatitis B surface antigen (HBsAg) may affect the antigenicity and immunogenicity of HBsAg, leading to immune escape and diagnostic failure. The amino acid positions 122 and 160 are known as determinants for HBsAg subtypes d/y and w/r, respectively. The substitution K122I has been shown to strongly affect HBsAg antigenicity. In this study, we investigated the significance of naturally occurring amino acid substitutions K122I, T123N, A159G and K160N. Both T123N and K160N substitutions resulted in additional N-glycosylated forms of HBsAg, while the other mutations produced more glycosylated HBsAg compared with the wild type (wt). Detection of HBsAg by ELISA and immunofluorescence staining indicated that variant HBsAg (vtHBsAg) with K122I was not recognized by HBsAg immunoassays, while vtHBsAg with T123N, A159G, K160N and A159G/K160N had reduced antigenicity. DNA immunization in BALB/c mice revealed that wtHBsAg and vtHBsAg with T123N and K160N are able to induce antibodies to HBsAg (anti-HBs), whereas K122I and A159G greatly impair the ability of HBsAg to trigger anti-HBs responses. The cellular immune response to the HBsAg aa 29-38 epitope was enhanced by the K160N substitution. Using replication competent clones of hepatitis B virus (HBV), T123N and A159G substitutions were shown to strongly reduce virion assembly. The amino acid substitution K160N appeared to compensate for the negative effect of A159G on virion production. These results reveal complex effects of amino acid substitutions on biochemical properties of HBsAg, on antigenicity and immunogenicity, and on the replication of HBV.