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Characterization of a Novel Conformational GII.4 Norovirus Epitope: Implications for Norovirus-Host Interactions.

ABSTRACT: Human noroviruses (NoVs) are the main etiological agents of acute gastroenteritis worldwide. While NoVs are highly diverse (more than 30 genotypes have been detected in humans), during the last 40 years most outbreaks and epidemics have been caused by GII.4 genotype strains, raising questions about their persistence in the population. Among other potential explanations, immune evasion is considered to be a main driver of their success. In order to study antibody recognition and evasion in detail, we analyzed a conformational epitope recognized by a monoclonal antibody (3C3G3) by phage display, site-directed mutagenesis, and surface plasmon resonance. Our results show that the predicted epitope is composed of 11 amino acids within the P domain: P245, E247, I389, Q390, R397, R435, G443, Y444, P445, N446, and D448. Only two of them, R397 and D448, differ from the homologous variant (GII.4 Den-Haag_2006b) and from a previous variant (GII.4 VA387_1996) that is not recognized by the antibody. A double mutant derived from the VA387_1996 variant containing both changes, Q396R and N447D, is recognized by the 3C3G3 monoclonal antibody, confirming the participation of the two sites in the epitope recognized by the antibody. Furthermore, a single change, Q396R, is able to modify the histo-blood group antigen (HBGA) recognition pattern. These results provide evidence that the epitope recognized by the 3C3G3 antibody is involved in the virus-host interactions, both at the immunological and at the receptor levels.Human noroviruses are the main cause of viral diarrhea worldwide in people of all ages. Noroviruses can infect individuals who had been previously exposed to the same or different norovirus genotypes. Norovirus genotype GII.4 has been reported to be most prevalent during the last 40 years. In the present study, we describe a novel viral epitope identified by a monoclonal antibody and located within the highly diverse P domain of the capsid protein. The evolution of this epitope along with sequential GII.4 variants has allowed noroviruses to evade previously elicited antibodies, thus explaining how the GII.4 genotype can persist over long periods, reinfecting the population. Our results also show that the epitope participates in the recognition of host receptors that have evolved over time, as well.

SUBMITTER: Carmona-Vicente N

PROVIDER: S-EPMC4988155 | biostudies-literature | 2016 Sep

REPOSITORIES: biostudies-literature

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Characterization of a Novel Conformational GII.4 Norovirus Epitope: Implications for Norovirus-Host Interactions.

Carmona-Vicente Noelia N Vila-Vicent Susana S Allen David D Gozalbo-Rovira Roberto R Iturriza-Gómara Miren M Buesa Javier J Rodríguez-Díaz Jesús J

Journal of virology 20160812 17

<h4>Unlabelled</h4>Human noroviruses (NoVs) are the main etiological agents of acute gastroenteritis worldwide. While NoVs are highly diverse (more than 30 genotypes have been detected in humans), during the last 40 years most outbreaks and epidemics have been caused by GII.4 genotype strains, raising questions about their persistence in the population. Among other potential explanations, immune evasion is considered to be a main driver of their success. In order to study antibody recognition an ...[more]

PMID: 27307569

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Project description:Extensive antigenic diversity within the GII.4 genotype of human norovirus is a major driver of pandemic emergence and a significant obstacle to development of cross-protective immunity after natural infection and vaccination. However, human and mouse monoclonal antibody studies indicate that, although rare, antibodies to conserved GII.4 blockade epitopes are generated. The mechanisms by which these epitopes evade immune surveillance are uncertain. Here, we developed a new approach for identifying conserved GII.4 norovirus epitopes. Utilizing a unique set of virus-like particles (VLPs) representing the in vivo-evolved sequence diversity within an immunocompromised person, we identify key residues within epitope F, a conserved GII.4 blockade antibody epitope. The residues critical for antibody binding are proximal to evolving blockade epitope E. Like epitope F, antibody blockade of epitope E was temperature sensitive, indicating that particle conformation regulates antibody access not only to the conserved GII.4 blockade epitope F but also to the evolving epitope E. These data highlight novel GII.4 mechanisms to protect blockade antibody epitopes, map essential residues of a GII.4 conserved epitope, and expand our understanding of how viral particle dynamics may drive antigenicity and antibody-mediated protection by effectively shielding blockade epitopes. Our data support the notion that GII.4 particle breathing may well represent a major mechanism of humoral immune evasion supporting cyclic pandemic virus persistence and spread in human populations. IMPORTANCE In this study, we use norovirus virus-like particles to identify key residues of a conserved GII.4 blockade antibody epitope. Further, we identify an additional GII.4 blockade antibody epitope to be occluded, with antibody access governed by temperature and particle dynamics. These findings provide additional support for particle conformation-based presentation of binding residues mediated by a particle "breathing core." Together, these data suggest that limiting antibody access to blockade antibody epitopes may be a frequent mechanism of immune evasion for GII.4 human noroviruses. Mapping blockade antibody epitopes, the interaction between adjacent epitopes on the particle, and the breathing core that mediates antibody access to epitopes provides greater mechanistic understanding of epitope camouflage strategies utilized by human viral pathogens to evade immunity.

Project description:GII.4 noroviruses (NoVs) are the primary cause of epidemic viral acute gastroenteritis. One primary obstacle to successful NoV vaccination is the extensive degree of antigenic diversity among strains. The major capsid protein of GII.4 strains is evolving rapidly, resulting in the emergence of new strains with altered blockade epitopes. In addition to characterizing these evolving blockade epitopes, we have identified monoclonal antibodies (MAbs) that recognize a blockade epitope conserved across time-ordered GII.4 strains. Uniquely, the blockade potencies of MAbs that recognize the conserved GII.4 blockade epitope were temperature sensitive, suggesting that particle conformation may regulate functional access to conserved blockade non-surface-exposed epitopes. To map conformation-regulating motifs, we used bioinformatics tools to predict conserved motifs within the protruding domain of the capsid and designed mutant VLPs to test the impacts of substitutions in these motifs on antibody cross-GII.4 blockade. Charge substitutions at residues 310, 316, 484, and 493 impacted the blockade potential of cross-GII.4 blockade MAbs with minimal impact on the blockade of MAbs targeting other, separately evolving blockade epitopes. Specifically, residue 310 modulated antibody blockade temperature sensitivity in the tested strains. These data suggest access to the conserved GII.4 blockade antibody epitope is regulated by particle conformation, temperature, and amino acid residues positioned outside the antibody binding site. The regulating motif is under limited selective pressure by the host immune response and may provide a robust target for broadly reactive NoV therapeutics and protective vaccines.In this study, we explored the factors that govern norovirus (NoV) cross-strain antibody blockade. We found that access to the conserved GII.4 blockade epitope is regulated by temperature and distal residues outside the antibody binding site. These data are most consistent with a model of NoV particle conformation plasticity that regulates antibody binding to a distally conserved blockade epitope. Further, antibody "locking" of the particle into an epitope-accessible conformation prevents ligand binding, providing a potential target for broadly effective drugs. These observations open lines of inquiry into the mechanisms of human NoV entry and uncoating, fundamental biological questions that are currently unanswerable for these noncultivatable pathogens.

Dataset Information

Characterization of a Novel Conformational GII.4 Norovirus Epitope: Implications for Norovirus-Host Interactions.

Publications

Characterization of a Novel Conformational GII.4 Norovirus Epitope: Implications for Norovirus-Host Interactions.

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