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Cryo-electron Microscopy Structures of Chimeric Hemagglutinin Displayed on a Universal Influenza Vaccine Candidate.

ABSTRACT: UNLABELLED:Influenza viruses expressing chimeric hemagglutinins (HAs) are important tools in the quest for a universal vaccine. Using cryo-electron tomography, we have determined the structures of a chimeric HA variant that comprises an H1 stalk and an H5 globular head domain (cH5/1 HA) in native and antibody-bound states. We show that cH5/1 HA is structurally different from native HA, displaying a 60° rotation between the stalk and head groups, leading to a novel and unexpected "open" arrangement of HA trimers. cH5/1N1 viruses also display higher glycoprotein density than pH1N1 or H5N1 viruses, but despite these differences, antibodies that target either the stalk or head domains of hemagglutinins still bind to cH5/1 HA with the same consequences as those observed with native H1 or H5 HA. Our results show that a large range of structural plasticity can be tolerated in the chimeric spike scaffold without disrupting structural and geometric aspects of antibody binding. IMPORTANCE:Chimeric hemagglutinin proteins are set to undergo human clinical trials as a universal influenza vaccine candidate, yet no structural information for these proteins is available. Using cryo-electron tomography, we report the first three-dimensional (3D) visualization of chimeric hemagglutinin proteins displayed on the surface of the influenza virus. We show that, unexpectedly, the chimeric hemagglutinin structure differs from those of naturally occurring hemagglutinins by displaying a more open head domain and a dramatically twisted head/stalk arrangement. Despite this unusual spatial relationship between head and stalk regions, virus preparations expressing the chimeric hemagglutinin are fully infectious and display a high glycoprotein density, which likely helps induction of a broadly protective immune response.

SUBMITTER: Tran EE

PROVIDER: S-EPMC4807363 | biostudies-literature | 2016 Mar

REPOSITORIES: biostudies-literature

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Cryo-electron Microscopy Structures of Chimeric Hemagglutinin Displayed on a Universal Influenza Vaccine Candidate.

Tran Erin E H EE Podolsky Kira A KA Bartesaghi Alberto A Kuybeda Oleg O Grandinetti Giovanna G Wohlbold Teddy John TJ Tan Gene S GS Nachbagauer Raffael R Palese Peter P Krammer Florian F Subramaniam Sriram S

mBio 20160322 2

<h4>Unlabelled</h4>Influenza viruses expressing chimeric hemagglutinins (HAs) are important tools in the quest for a universal vaccine. Using cryo-electron tomography, we have determined the structures of a chimeric HA variant that comprises an H1 stalk and an H5 globular head domain (cH5/1 HA) in native and antibody-bound states. We show that cH5/1 HA is structurally different from native HA, displaying a 60° rotation between the stalk and head groups, leading to a novel and unexpected "open" a ...[more]

PMID: 27006464

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Project description:The capsid protein (VP1) of all caliciviruses forms an icosahedral particle with two principal domains, shell (S) and protruding (P) domains, which are connected via a flexible hinge region. The S domain forms a scaffold surrounding the nucleic acid, while the P domains form a homodimer that interacts with receptors. The P domain is further subdivided into two subdomains, termed P1 and P2. The P2 subdomain is likely an insertion in the P1 subdomain; consequently, the P domain is divided into the P1-1, P2, and P1-2 subdomains. In order to investigate capsid antigenicity, N-terminal (N-term)/S/P1-1 and P2/P1-2 were switched between two sapovirus genotypes GI.1 and GI.5. The chimeric VP1 constructs were expressed in insect cells and were shown to self-assemble into virus-like particles (VLPs) morphologically similar to the parental VLPs. Interestingly, the chimeric VLPs had higher levels of cross-reactivities to heterogeneous antisera than the parental VLPs. In order to better understand the antigenicity from a structural perspective, we determined an intermediate-resolution (8.5-Å) cryo-electron microscopy (cryo-EM) structure of a chimeric VLP and developed a VP1 homology model. The cryo-EM structure revealed that the P domain dimers were raised slightly (?5 Å) above the S domain. The VP1 homology model allowed us predict the S domain (67-229) and P1-1 (229-280), P2 (281-447), and P1-2 (448-567) subdomains. Our results suggested that the raised P dimers might expose immunoreactive S/P1-1 subdomain epitopes. Consequently, the higher levels of cross-reactivities with the chimeric VLPs resulted from a combination of GI.1 and GI.5 epitopes.We developed sapovirus chimeric VP1 constructs and produced the chimeric VLPs in insect cells. We found that both chimeric VLPs had a higher level of cross-reactivity against heterogeneous VLP antisera than the parental VLPs. The cryo-EM structure of one chimeric VLP (Yokote/Mc114) was solved to 8.5-Å resolution. A homology model of the VP1 indicated for the first time the putative S and P (P1-1, P2, and P1-2) domains. The overall structure of Yokote/Mc114 contained features common among other caliciviruses. We showed that the P2 subdomain was mainly involved in the homodimeric interface, whereas a large gap between the P1 subdomains had fewer interactions.

Dataset Information

Cryo-electron Microscopy Structures of Chimeric Hemagglutinin Displayed on a Universal Influenza Vaccine Candidate.

Publications

Cryo-electron Microscopy Structures of Chimeric Hemagglutinin Displayed on a Universal Influenza Vaccine Candidate.

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