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A calcium sensor discovered in Bluetongue virus non-structural protein 2 is critical for virus replication.

ABSTRACT: Many viruses use specific viral proteins to bind calcium ions (Ca2+) for stability or to modify host cell pathways, however, to date no Ca2+ binding protein has been reported in Bluetongue virus (BTV), the causative agent of Bluetongue disease in livestock. Here, using a comprehensive bioinformatics screening, we identified a putative EF-hand-like Ca2+ binding motif in the carboxyl terminal region of BTV non-structural phosphoprotein 2 (NS2). Subsequently, using a recombinant NS2, we demonstrated that NS2 binds Ca2+ efficiently and that Ca2+ binding was perturbed when the Asp and Glu residues in the motif were substituted by Alanine. Using Circular dichroism analysis, we found that Ca2+ binding by NS2 triggered a helix-to-coil secondary structure transition. Further, cryo-electron microscopy in presence of Ca2+, revealed that NS2 forms helical oligomers which, when aligned with the N-terminal domain crystal structure, suggest an N-terminal domain which wraps around the C-terminal domain in the oligomer. Further, an in vitro kinase assay demonstrated that Ca2+ enhanced the phosphorylation of NS2 significantly. Importantly, mutations introduced at the Ca2+ binding site in the viral genome by reverse genetics failed to allow recovery of viable virus and that the NS2 phosphorylation level and assembly of VIBs were reduced. Together, our data suggest that NS2 is a dedicated Ca2+ binding protein and that calcium sensing acts as a trigger for VIB assembly, which in turn facilitates virus replication and assembly.IMPORTANCE After entering the host cells viruses use cellular host factors to ensure a successful virus replication process. For replication in infected cells members of Reoviridae family form an inclusion body like structure known as viral inclusion bodies (VIB) or viral factories. Bluetongue virus (BTV) forms VIBs in infected cells through non-structural protein 2 (NS2), a phosphoprotein. An important regulatory factor critical for VIB formation is phosphorylation of NS2. In our study, we discovered a characteristic calcium binding EF hand like motif in NS2 and found that the calcium binding preferentially affects phosphorylation level of the NS2 and has a role in regulating VIB assembly.

SUBMITTER: Rahman SK

PROVIDER: S-EPMC7116143 | biostudies-literature | 2020 Aug

REPOSITORIES: biostudies-literature

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A Calcium Sensor Discovered in Bluetongue Virus Nonstructural Protein 2 Is Critical for Virus Replication.

Rahman Shah Kamranur SK Kerviel Adeline A Mohl Bjorn-Patrick BP He Yao Y Zhou Z Hong ZH Roy Polly P

Journal of virology 20200929 20

Many viruses use specific viral proteins to bind calcium ions (Ca2+) for stability or to modify host cell pathways; however, to date, no Ca2+ binding protein has been reported in bluetongue virus (BTV), the causative agent of bluetongue disease in livestock. Here, using a comprehensive bioinformatics screening, we identified a putative EF-hand-like Ca2+ binding motif in the carboxyl terminal region of BTV nonstructural phosphoprotein 2 (NS2). Subsequently, using ...[more]

PMID: 32759321

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Project description:Many viruses use specific viral proteins to bind calcium ions (Ca2+) for stability or to modify host cell pathways; however, to date, no Ca2+ binding protein has been reported in bluetongue virus (BTV), the causative agent of bluetongue disease in livestock. Here, using a comprehensive bioinformatics screening, we identified a putative EF-hand-like Ca2+ binding motif in the carboxyl terminal region of BTV nonstructural phosphoprotein 2 (NS2). Subsequently, using a recombinant NS2, we demonstrated that NS2 binds Ca2+ efficiently and that Ca2+ binding was perturbed when the Asp and Glu residues in the motif were substituted by alanine. Using circular dichroism analysis, we found that Ca2+ binding by NS2 triggered a helix-to-coil secondary structure transition. Further, cryo-electron microscopy in the presence of Ca2+ revealed that NS2 forms helical oligomers which, when aligned with the N-terminal domain crystal structure, suggest an N-terminal domain that wraps around the C-terminal domain in the oligomer. Further, an in vitro kinase assay demonstrated that Ca2+ enhanced the phosphorylation of NS2 significantly. Importantly, mutations introduced at the Ca2+ binding site in the viral genome by reverse genetics failed to allow recovery of viable virus, and the NS2 phosphorylation level and assembly of viral inclusion bodies (VIBs) were reduced. Together, our data suggest that NS2 is a dedicated Ca2+ binding protein and that calcium sensing acts as a trigger for VIB assembly, which in turn facilitates virus replication and assembly.IMPORTANCE After entering the host cells, viruses use cellular host factors to ensure a successful virus replication process. For replication in infected cells, members of the Reoviridae family form inclusion body-like structures known as viral inclusion bodies (VIB) or viral factories. Bluetongue virus (BTV) forms VIBs in infected cells through nonstructural protein 2 (NS2), a phosphoprotein. An important regulatory factor critical for VIB formation is phosphorylation of NS2. In our study, we discovered a characteristic calcium-binding EF-hand-like motif in NS2 and found that the calcium binding preferentially affects phosphorylation level of the NS2 and has a role in regulating VIB assembly.

Project description:Bluetongue virus (BTV) causes non-contagious haemorrhagic disease in ruminants and is transmitted by Culicoides spp. biting midges. BTV encodes four non-structural proteins of which NS3/NS3a is functional in virus release. NS3/NS3a is not essential for in vitro virus replication. However, deletion of NS3/NS3a leads to delayed virus release from mammalian cells and largely reduces virus release from insect cells. NS3/NS3a knockout BTV in sheep causes no viremia, but induces sterile immunity and is therefore proposed to be a Disabled Infectious Single Animal (DISA) vaccine candidate. In the absence of viremia, uptake of this vaccine strain by blood-feeding midges would be highly unlikely. Nevertheless, unintended replication of vaccine strains within vectors, and subsequent recombination or re-assortment resulting in virulent phenotypes and transmission is a safety concern of modified-live vaccines.The role of NS3/NS3a in replication and dissemination of BTV1, expressing VP2 of serotype 2 within colonized Culicoides sonorensis midges was investigated. Virus strains were generated using reverse genetics and their growth was examined in vitro. A laboratory colony of C. sonorensis, a known competent BTV vector, was fed or injected with BTV with or without expressing NS3/NS3a and replication in the midge was examined using RT PCR. Crossing of the midgut infection barrier was examined by separate testing of midge heads and bodies.Although the parental NS3/NS3a expressing strain was not able to replicate and disseminate within C. sonorensis after oral feeding, this virus was able to replicate efficiently when the midgut infection barrier was bypassed by intrathoracic injection, whereas the NS3/NS3a knockout mutant was unable to replicate. This demonstrates that NS3/NS3a is required for viral replication within Culicoides.The lack of viremia and the inability to replicate within the vector, clearly demonstrate the inability of NS3/NS3a knockout DISA vaccine strains to be transmitted by midges.

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A calcium sensor discovered in Bluetongue virus non-structural protein 2 is critical for virus replication.

Publications

A Calcium Sensor Discovered in Bluetongue Virus Nonstructural Protein 2 Is Critical for Virus Replication.

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