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Probing Zika Virus Neutralization Determinants with Glycoprotein Mutants Bearing Linear Epitope Insertions.

ABSTRACT: Zika virus (ZIKV) glycoproteins are the primary target of the humoral immune response. In this study, we explored the capacity of these glycoproteins to tolerate insertion of linear epitope sequences and the potential of antibodies that bind these epitopes to inhibit infection. We first created a panel of ZIKV mutants with the FLAG epitope inserted in the premembrane (prM) and envelope (E) glycoprotein regions. The insertion locations were based on the results of our recent transposon insertional mutagenesis screen. Although FLAG insertions in prM greatly impaired viral fitness, this sequence was tolerated in numerous surface-exposed E protein sites. We observed that mutants bearing FLAG epitopes in E domains I and II and the E domain I-II hinge region were all neutralized by FLAG antibody; however, the neutralization sensitivity varied highly. We measured the antibody binding efficiency and found that this closely matched the pattern of neutralization sensitivity. We determined that E glycosylation did not affect antibody binding to a nearby epitope or its capacity to serve as a neutralization target. Although we could not generate infectious viruses with FLAG epitope insertions in a buried region of E protein domain III, we found that the V5 epitope could be inserted at this site without greatly impacting fitness. Furthermore, this virus was efficiently neutralized by V5 antibodies, highlighting that even buried epitopes can function as neutralization targets. Finally, we analyzed the timing of antibody neutralization activity during cell entry and found that all antibodies blocked a step after cell attachment.IMPORTANCE Zika virus (ZIKV) infections are associated with severe birth defects and neurological disease. The structure of the mature ZIKV particle reveals a virion surface covered by the envelope glycoprotein, which is the dominant target of the humoral immune response. It is unclear if all regions of the envelope protein surface or even buried epitopes can function as neutralization targets. To test this, we created a panel of ZIKV mutants with epitope insertions in different regions of the envelope protein. In characterizing these viruses, we found that the strength of antibody binding to an epitope is the major determinant of the neutralization potential of an antibody, that even a buried region of the envelope protein can be efficiently targeted, and that the sole potential envelope glycan does not impact nearby epitope antibody binding and neutralization. Furthermore, this work provides important insights into our understanding of how antibodies neutralize ZIKV.

SUBMITTER: Chambers MT

PROVIDER: S-EPMC6146680 | biostudies-literature | 2018 Sep

REPOSITORIES: biostudies-literature

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Probing Zika Virus Neutralization Determinants with Glycoprotein Mutants Bearing Linear Epitope Insertions.

Chambers Matthew T MT Schwarz Megan C MC Sourisseau Marion M Gray Essanna S ES Evans Matthew J MJ

Journal of virology 20180829 18

Zika virus (ZIKV) glycoproteins are the primary target of the humoral immune response. In this study, we explored the capacity of these glycoproteins to tolerate insertion of linear epitope sequences and the potential of antibodies that bind these epitopes to inhibit infection. We first created a panel of ZIKV mutants with the FLAG epitope inserted in the premembrane (prM) and envelope (E) glycoprotein regions. The insertion locations were based on the results of our recent transposon insertiona ...[more]

PMID: 29976678

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Project description:Human herpesvirus 6A (HHV-6A) glycoprotein B (gB) is a glycoprotein consisting of 830 amino acids and is essential for the growth of the virus. Previously, we reported that a neutralizing monoclonal antibody (MAb) called 87-y-13 specifically reacts with HHV-6A gB, and we identified its epitope residue at asparagine (Asn) 347 on gB. In this study, we examined whether the epitope recognized by the neutralizing MAb is essential for HHV-6A infection. We constructed HHV-6A bacterial artificial chromosome (BAC) genomes harboring substitutions at Asn347, namely, HHV-6A BACgB(N347K) and HHV-6A BACgB(N347A). These mutant viruses could be reconstituted and propagated in the same manner as the wild type and their revertants, and MAb 87-y-13 could not inhibit infection by either mutant. In a cell-cell fusion assay, Asn at position 347 on gB was found to be nonessential for cell-cell fusion. In addition, in building an HHV-6A gB homology model, we found that the epitope of the neutralizing MAb is located on domain II of gB and is accessible to solvents. These results indicate that Asn at position 347, the linear epitope of the neutralizing MAb, does not affect HHV-6A infectivity.IMPORTANCE Glycoprotein B (gB) is one of the most conserved glycoproteins among all herpesviruses and is a key factor for virus entry. Therefore, antibodies targeted to gB may neutralize virus entry. Human herpesvirus 6A (HHV-6A) encodes gB, which is translated to a protein of about 830 amino acids (aa). Using a monoclonal antibody (MAb) for HHV-6A gB, which has a neutralizing linear epitope, we analyzed the role of its epitope residue, N347, in HHV-6A infectivity. Interestingly, this gB linear epitope residue, N347, was not essential for HHV-6A growth. By constructing a homology model of HHV-6A gB, we found that N347 was located in the region corresponding to domain II. Therefore, with regard to its neutralizing activity against HHV-6A infection, the epitope on gB might be exposed to solvents, suggesting that it might be a target of the immune system.

Project description:Dengue and Zika are two mosquito-borne diseases of great concern, affecting mainly the tropical and subtropical regions worldwide. The arrival of Zika virus (ZIKV) in dengue virus (DENV) endemic areas imposed challenges for differential diagnosis and the development of candidate vaccines. The use of peptides has shown great potential to achieve these goals. We aimed to identify the linear epitope profile recognized by the serum samples of dengue and Zika patients in the E and NS1 proteins of DENV and ZIKV to select peptides with the potential for the development of diagnostic tests and vaccines. Analysis of a peptide microarray platform with serum samples of dengue and Zika patients demonstrated that the epitopes were evenly distributed across the entire viral proteins, showing no preference for particular regions. However, several epitopes were within epitope hot spots constituted by clusters of peptides recognized in more than 30% of the sub-arrays analyzed with individual or pools of serum samples. The serum samples of dengue and Zika patients showed a high level of cross-reaction for epitopes in the DENV and ZIKV proteins. Analysis of an additional peptide microarray platform containing selected peptides based on the results of the first screening showed that three peptides (DENV: TQGEPSLNEEQDKRF and TQTVGPWHLGKLEID; ZIKV: LELDPPFGDSYIVIG), highly specific for their cognate viruses (p<0.05), were within the epitope hot spots; however, these peptides showed low detection rates (32.5, 35.0, and 28.6%, respectively). We also found two peptides (DENV: WEVEDYGFGVFTTNI and LELDFDLCEGTTVVV) in the epitope hot spots detected by both dengue and Zika patients with similarly high rates (arbitrary detection rate cut-off threshold of ≥40%). The epitope hot spots harbor several immunodominant epitopes recognized by a higher number of individuals when compared to the 15 aa sequence peptides. Therefore, the entire epitope hot spots, spanning up to ~30 aa, would have more potential than peptides of only 15 aa to serve as antigens in diagnostic tests and vaccine developments.

Dataset Information

Probing Zika Virus Neutralization Determinants with Glycoprotein Mutants Bearing Linear Epitope Insertions.

Publications

Probing Zika Virus Neutralization Determinants with Glycoprotein Mutants Bearing Linear Epitope Insertions.

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