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Li Z, Zhang N, Zhang T, Wang Z, Li J, Wang M, Hu Z, Wang X. AcMNPV P74 is cleaved at R325 and R334 by proteinases of both OB and BBMV to expose a potential fusion peptide for oral infection. J Virol 2024; 98:e0023524. [PMID: 38775478 DOI: 10.1128/jvi.00235-24] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2024] [Accepted: 04/27/2024] [Indexed: 06/14/2024] Open
Abstract
Baculoviruses enter insect midgut epithelial cells via a set of occlusion-derived virion (ODV) envelope proteins called per os infectivity factors (PIFs). P74 of Autographa californica multicapsid nucleopolyhedrovirus (AcMNPV), which was the first identified PIF, is cleaved by an endogenous proteinase embedded within the occlusion body during per os infection, but the target site(s) and function of the cleavage have not yet been ascertained. Here, based on bioinformatics analyses, we report that cleavage was predicted at an arginine and lysine-rich region in the middle of P74. A series of recombinant viruses with site-directed mutants in this region of P74 were generated. R325 or R334 was identified as primary cleavage site. In addition, we showed that P74 is also cleaved by brush border membrane vesicles (BBMV) of the host insect at R325 or R334, instead of R195, R196, and R199, as previously reported. Simultaneous mutations in R195, R196, and R199 lead to instability of P74 during ODV release. Bioassays showed that mutations at both R325 and R334 significantly affected oral infectivity. Taken together, our data show that both R325 and R334 of AcMNPV P74 are the primary cleavage site for both occlusion body endogenous proteinase and BBMV proteinase during ODV release and are critical for oral infection. IMPORTANCE Cleavage of viral envelope proteins is usually an important trigger for viral entry into host cells. Baculoviruses are insect-specific viruses that infect host insects via the oral route. P74, a per os infectivity factor of baculoviruses, is cleaved during viral entry. However, the function and precise cleavage sites of P74 remain unknown. In this study, we found that R325 or R334 between the N- and C-conserved domains of P74 was the primary cleavage site by proteinase either from the occlusion body or host midgut. The biological significance of cleavage seems to be the release of the potential fusion peptide at the N-terminus of the cleaved C-terminal P74. Our results shed light on the cleavage model of P74 and imply its role in membrane fusion in baculovirus per os infection.
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Affiliation(s)
- Zhuorui Li
- Key Laboratory of Virology and Biosafety, Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, China
- University of Chinese Academy of Sciences, Beijing, China
| | - Nan Zhang
- Key Laboratory of Virology and Biosafety, Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, China
| | - Tao Zhang
- Key Laboratory of Virology and Biosafety, Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, China
| | - Zhiying Wang
- Key Laboratory of Virology and Biosafety, Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, China
| | - Jiang Li
- Key Laboratory of Virology and Biosafety, Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, China
| | - Manli Wang
- Key Laboratory of Virology and Biosafety, Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, China
| | - Zhihong Hu
- Key Laboratory of Virology and Biosafety, Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, China
| | - Xi Wang
- Key Laboratory of Virology and Biosafety, Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, China
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Jia X, Gao Y, Huang Y, Sun L, Li S, Li H, Zhang X, Li Y, He J, Wu W, Venkannagari H, Yang K, Baker ML, Zhang Q. Architecture of the baculovirus nucleocapsid revealed by cryo-EM. Nat Commun 2023; 14:7481. [PMID: 37980340 PMCID: PMC10657434 DOI: 10.1038/s41467-023-43284-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2023] [Accepted: 11/03/2023] [Indexed: 11/20/2023] Open
Abstract
Baculovirus Autographa californica multiple nucleopolyhedrovirus (AcMNPV) has been widely used as a bioinsecticide and a protein expression vector. Despite their importance, very little is known about the structure of most baculovirus proteins. Here, we show a 3.2 Å resolution structure of helical cylindrical body of the AcMNPV nucleocapsid, composed of VP39, as well as 4.3 Å resolution structures of both the head and the base of the nucleocapsid composed of over 100 protein subunits. AcMNPV VP39 demonstrates some features of the HK97-like fold and utilizes disulfide-bonds and a set of interactions at its C-termini to mediate nucleocapsid assembly and stability. At both ends of the nucleocapsid, the VP39 cylinder is constricted by an outer shell ring composed of proteins AC104, AC142 and AC109. AC101(BV/ODV-C42) and AC144(ODV-EC27) form a C14 symmetric inner layer at both capsid head and base. In the base, these proteins interact with a 7-fold symmetric capsid plug, while a portal-like structure is seen in the central portion of head. Additionally, we propose an application of AlphaFold2 for model building in intermediate resolution density.
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Affiliation(s)
- Xudong Jia
- State key laboratory of biocontrol, School of Life Sciences, Sun Yat-sen University, 510275, Guangzhou, China
| | - Yuanzhu Gao
- State key laboratory of biocontrol, School of Life Sciences, Sun Yat-sen University, 510275, Guangzhou, China
- Cryo-EM Facility Center, Southern University of Science and Technology, Shenzhen, China
| | - Yuxuan Huang
- State key laboratory of biocontrol, School of Life Sciences, Sun Yat-sen University, 510275, Guangzhou, China
| | - Linjun Sun
- State key laboratory of biocontrol, School of Life Sciences, Sun Yat-sen University, 510275, Guangzhou, China
| | - Siduo Li
- State key laboratory of biocontrol, School of Life Sciences, Sun Yat-sen University, 510275, Guangzhou, China
| | - Hongmei Li
- State key laboratory of biocontrol, School of Life Sciences, Sun Yat-sen University, 510275, Guangzhou, China
| | - Xueqing Zhang
- State key laboratory of biocontrol, School of Life Sciences, Sun Yat-sen University, 510275, Guangzhou, China
| | - Yinyin Li
- State key laboratory of biocontrol, School of Life Sciences, Sun Yat-sen University, 510275, Guangzhou, China
| | - Jian He
- State key laboratory of biocontrol, School of Life Sciences, Sun Yat-sen University, 510275, Guangzhou, China
| | - Wenbi Wu
- State key laboratory of biocontrol, School of Life Sciences, Sun Yat-sen University, 510275, Guangzhou, China
| | - Harikanth Venkannagari
- Department of Biochemistry and Molecular Biology, McGovern Medical School at the University of Texas Health Science Center, Houston, TX, 77030, USA
| | - Kai Yang
- State key laboratory of biocontrol, School of Life Sciences, Sun Yat-sen University, 510275, Guangzhou, China
| | - Matthew L Baker
- Department of Biochemistry and Molecular Biology, McGovern Medical School at the University of Texas Health Science Center, Houston, TX, 77030, USA.
| | - Qinfen Zhang
- State key laboratory of biocontrol, School of Life Sciences, Sun Yat-sen University, 510275, Guangzhou, China.
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Abstract
White spot syndrome virus (WSSV) is a major cause of disease in shrimp cultures worldwide. The infection process of this large circular double-stranded DNA virus has been well studied, but its entry mechanism remains controversial. The major virion envelope protein VP28 has been implicated in oral and systemic viral infection in shrimp. However, genetic analysis of viral DNA has shown the presence of a few genes related to proteins of per os infectivity factor (PIF) complex in baculoviruses. This complex is essential for the entry of baculoviruses, large terrestrial circular DNA viruses, into the midgut epithelial cells of insect larvae. In this study, we aimed to determine whether a PIF complex exists in WSSV, the components of this complex, whether it functions as an oral infectivity complex in shrimp, and the biochemical properties that contribute to its function in a marine environment. The results revealed a WSSV PIF complex (~720 kDa) comprising at least eight proteins, four of which were not identified as PIF homologs: WSV134, VP124 (WSV216), WSSV021, and WSV136. WSV134 is suggested to be a PIF4 homolog due to predicted structural similarity and amino acid sequence identity. The WSSV PIF complex is resistant to alkali, proteolysis, and high salt, properties that are important for maintaining infectivity in aquatic environments. Oral infection can be neutralized by PIF-specific antibodies but not by VP28-specific antibodies. These results indicate that the WSSV PIF complex is critical for WSSV entry into shrimp; the complex's evolutionary significance is also discussed. IMPORTANCE White spot disease, caused by the white spot syndrome virus (WSSV), is a major scourge in cultured shrimp production facilities worldwide. This disease is only effectively controlled by sanitation. Intervention strategies are urgently needed but are limited by a lack of appropriate targets. Our identification of a per os infectivity factor (PIF) complex, which is pivotal for the entry of WSSV into shrimp, could provide new targets for antibody- or dsRNA-based intervention strategies. In addition, the presence of a PIF complex with at least eight components in WSSV, which is ancestrally related to the PIF complex of invertebrate baculoviruses, suggests that this complex is structurally and functionally conserved in disparate virus taxa.
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AC81 Is a Putative Disulfide Isomerase Involved in Baculoviral Disulfide Bond Formation. J Virol 2022; 96:e0116722. [PMID: 36468861 PMCID: PMC9769380 DOI: 10.1128/jvi.01167-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
The correct formation of native disulfide bonds is critical for the proper structure and function of many proteins. Cellular disulfide bond formation pathways commonly consist of two parts: sulfhydryl oxidase-mediated oxidation and disulfide isomerase-mediated isomerization. Some large DNA viruses, such as baculoviruses, encode sulfhydryl oxidases, but viral disulfide isomerases have not yet been identified, although G4L in poxvirus has been suggested to serve such a function. Here, we report that the baculovirus core gene ac81 encodes a putative disulfide isomerase. ac81 is conserved in baculoviruses, nudiviruses, and hytrosaviruses. We found that AC81 homologs contain a typical thioredoxin fold conserved in disulfide isomerases. To determine the role of AC81, a series of Autographa californica nucleopolyhedrovirus (AcMNPV) bacmids containing ac81 knockout or point mutations was generated, and the results showed that AC81 is essential for budded virus production, multinucleocapsid occlusion-derived virus (ODV) formation, and ODV embedding in occlusion bodies. Nonreducing Western blot analysis indicated that disulfide bond formation in per os infectivity factor 5 (PIF5), a substrate of the baculoviral sulfhydryl oxidase P33, was abnormal when ac81 was knocked out or mutated. Pulldown assays showed that AC81 interacted with PIF5 and P33 in infected cells. In addition, two critical regions that harbor key amino acids for function were identified in AC81. Taken together, our results suggest that AC81 is a key component involved in the baculovirus disulfide bond formation pathway and likely functions as a disulfide isomerase. IMPORTANCE Many large DNA viruses, such as poxvirus, asfarvirus, and baculovirus, encode their own sulfhydryl oxidase to facilitate the disulfide bond formation of viral proteins. Here, we show that AC81 functions as a putative disulfide isomerase and is involved in multiple functions of the baculovirus life cycle. Interestingly, AC81 and P33 (sulfhydryl oxidase) are conserved in baculoviruses, nudiviruses, and hytrosaviruses, which are all insect-specific large DNA viruses replicating in the nucleus, suggesting that viral disulfide bond formation is an ancient mechanism shared by these viruses.
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