Comparative Proteomics Reveal Fundamental Structural and Functional Differences between the Two Progeny Phenotypes of a Baculovirus

Abstract

The replication of lepidopteran baculoviruses is characterized by the production of two progeny phenotypes: the occlusion-derived virus (ODV), which establishes infection in midgut cells, and the budded virus (BV), which disseminates infection to different tissues within a susceptible host. To understand the structural, and hence functional, differences between BV and ODV, we employed multiple proteomic methods to reveal the protein compositions and posttranslational modifications of the two phenotypes of Helicoverpa armigera nucleopolyhedrovirus. In addition, Western blotting and quantitative mass spectrometry were used to identify the localization of proteins in the envelope or nucleocapsid fractions. Comparative protein portfolios of BV and ODV showing the distribution of 54 proteins, encompassing the 21 proteins shared by BV and ODV, the 12 BV-specific proteins, and the 21 ODV-specific proteins, were obtained. Among the 11 ODV-specific envelope proteins, 8 either are essential for or contribute to oral infection. Twenty-three phosphorylated and 6 N-glycosylated viral proteins were also identified. While the proteins that are shared by the two phenotypes appear to be important for nucleocapsid assembly and trafficking, the structural and functional differences between the two phenotypes are evidently characterized by the envelope proteins and posttranslational modifications. This comparative proteomics study provides new insight into how BV and ODV are formed and why they function differently. Baculoviruses are insect-specific pathogens containing large circular double-stranded DNA genomes. Over millions of years of interdependence between viruses and their natural insect hosts, both have undergone a coevolution, such that lepidopteran baculoviruses have developed a unique biphasic replication cycle that generates two progeny phenotypes, the budded virus (BV) and the occlusion-derived virus (ODV). ODVs are embedded in occlusion bodies (OBs) that offer the virions a certain amount of protection against environmental degradation. Once ingested by a susceptible insect, ODVs are released from OBs within the larval midgut and initiate oral infection. After infecting midgut epithelial cells, BVs are synthesized and released to disseminate systemic infection of different tissues within the larval host. The two phenotypes have been used in a wide range of applications. Due to their expandable genome and the presence of very strong promoters, BVs have been established as successful vectors for the expression of thousands of proteins and have also been studied as potential vectors for gene therapy (1). The OBs of certain baculoviruses have been widely used in agriculture and forestry as viable alternatives to chemical insecticides in insect pest control (2).The broad applications of baculoviruses provide a strong rationale for identifying the proteins associated with both phenotypes and for understanding their roles in baculovirus infection. While previous proteomic studies have elucidated the protein compositions of a...

Proteomic analysis of the occlusion-derived virus of Clostera anachoreta granulovirus

“…Previous research suggested that ME53 may provide a scaffold that bridges the viral envelope and nucleocapsid (de Jong et al, 2011). As a common protein amongst the baculovirus genomes, ME53 was identified on the BVs of AcMNPV and HearNPV (Hou et al, 2013;Wang et al, 2010), whilst in this and PrGV studies it was identified as an ODV protein.…”

“…1). They covered 59.3 % of the complete theoretical proteome of ClanGV, which was a much higher percentage than those of other baculoviruses whose ODV compositions were successfully analysed by MS approaches (HearNPV, 42.2 %; CuniNPV, 41.3 %; PrGV, 39.2 %; ChchNPV, 35.1 %; AgMNPV, 28.9 %; AcMNPV, 28.6 %) (Braconi et al, 2014;Braunagel et al, 2003;Hou et al, 2013;Perera et al, 2007;Wang et al, 2011;Xu et al, 2011).…”

“…Noticeably, although no homologues of FGF-3 were detected in alphabaculoviruses by standard BLAST, it was not considered to be specific to betabaculovirus ODVs for three reasons: (i) FGF-like genes are present in almost all the baculovirus genomes, (ii) the HearNPV FGF has been identified as a BV component (Hou et al, 2013) and (iii) when one or more genomes have orthologues for the query protein, they might not be detected by standard methods because of their remote orthology. Recently, the number of baculovirus core genes was expanded from 29 to 37 by several bioinformatics approaches (Garavaglia et al, 2012).…”

“…These viruses include seven ODVs and three BVs: the ODVs of Autographa californica multiple nucleopolyhedrovirus (AcMNPV) (Braunagel et al, 2003), Helicoverpa armigera nucleopolyhedrovirus (HearNPV) (Hou et al, 2013), Anticarsia gemmatalis multiple nucleopolyhedrovirus (AgMNPV) (Braconi et al, 2014), Culex nigripalpus nucleopolyhedrovirus (CuniNPV) (Perera et al, 2007), Bombyx mori nucleopolyhedrovirus (BmNPV) (Liu et al, 2008), Chrysodeixis chalcites nucleopolyhedrovirus (ChchNPV) and Pieris rapae granulovirus (PrGV) (Wang et al, 2011); and the BVs of AcMNPV (Wang et al, 2010), HearNPV (Hou et al, 2013) and AgMNPV (Braconi et al, 2014). The numbers of proteins identified in these studies were 40,57,44,45,16,53,47,23,51 and 33, respectively.…”

Baculovirus nucleocapsid aggregation (MNPV vs SNPV): an evolutionary strategy, or a product of replication conditions?

“…It was found that AcMNPV deleted for ac23, an ortholog of the F fusion protein gene of Group II viruses (see above), shows an elevated percentage of singly enveloped virions, 45 % vs 11-22 % for different virus constructs that contained ac23 [19]. Although characterized as a BV-associated protein in AcMNPV [20], OpMNPV [21], and HearNPV [22], Ac23 was reported to be associated with AcMNPV ODV [23], suggesting that it could be directly involved in formation of the MNPV morphotype. Also a knockout (KO) of ac43 appeared to increase the number of SNPVs in occlusion bodies, and co-infection of the ac43 KO virus with a virus encoding ac43 restored the predominance of the MNPV morphotype [24].…”