[Source: PLoS Biology, full page: (LINK). Abstract, edited.]
OPEN ACCESS / PEER-REVIEWED / RESEARCH ARTICLE
Potent anti-influenza H7 human monoclonal antibody induces separation of hemagglutinin receptor-binding head domains
Hannah L. Turner , Jesper Pallesen , Shanshan Lang, Sandhya Bangaru, Sarah Urata, Sheng Li, Christopher A. Cottrell, Charles A. Bowman, James E. Crowe Jr., Ian A. Wilson, Andrew B. Ward
Published: February 4, 2019 / DOI: https://doi.org/10.1371/journal.pbio.3000139 / This is an uncorrected proof.
Seasonal influenza virus infections can cause significant morbidity and mortality, but the threat from the emergence of a new pandemic influenza strain might have potentially even more devastating consequences. As such, there is intense interest in isolating and characterizing potent neutralizing antibodies that target the hemagglutinin (HA) viral surface glycoprotein. Here, we use cryo-electron microscopy (cryoEM) to decipher the mechanism of action of a potent HA head-directed monoclonal antibody (mAb) bound to an influenza H7 HA. The epitope of the antibody is not solvent accessible in the compact, prefusion conformation that typifies all HA structures to date. Instead, the antibody binds between HA head protomers to an epitope that must be partly or transiently exposed in the prefusion conformation. The “breathing” of the HA protomers is implied by the exposure of this epitope, which is consistent with metastability of class I fusion proteins. This structure likely therefore represents an early structural intermediate in the viral fusion process. Understanding the extent of transient exposure of conserved neutralizing epitopes also may lead to new opportunities to combat influenza that have not been appreciated previously.
Influenza viruses cause severe respiratory infections on a global scale annually. Vaccine efforts are hampered by the virus’s naturally high mutation rate, which results in wide variation between influenza strains of the antigens that are produced and recognized by antibodies, particularly in the surface glycoprotein hemagglutinin (HA). However, broadly neutralizing antibodies (bnAbs) are a class of antibodies that develop during natural infections that are capable of inhibiting infection across multiple strains. In this study, we structurally characterized one such bnAb, H7.5, which targets a unique semioccluded yet highly conserved region on the HA head. We showed, using both negative-stain and high-resolution cryo-electron microscopy (cryoEM), that after a short incubation, H7.5 fragment antigen binding (Fab) induces HA to fall apart, effectively preventing infection. We found that H7.5 binds to an epitope only accessible through transient “breathing” of the HA head, and this observation provides insight into the conformational transitions necessary for viral fusion as well as key information about a unique vaccine target.
Citation: Turner HL, Pallesen J, Lang S, Bangaru S, Urata S, Li S, et al. (2019) Potent anti-influenza H7 human monoclonal antibody induces separation of hemagglutinin receptor-binding head domains. PLoS Biol 17(2): e3000139. https://doi.org/10.1371/journal.pbio.3000139
Academic Editor: James Conway, University of Pittsburgh, UNITED STATES
Received: September 28, 2018; Accepted: January 18, 2019; Published: February 4, 2019
Copyright: © 2019 Turner et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Data Availability: The final coordinates for the H7.5 Fab structure have been deposited to the RCSB database with the accession code PDB 6BTJ. The nsEM map of H7 NY HA1/2 complexed with 3 H7.5 Fabs bound, and the cryo-EM maps of H7 NL HA1/2 with 3 H7.5 Fabs bound, the H7 NL HA1/2 with 2 H7.5 Fabs bound, and the H7 Sh2 HA1/2 with 3 H7.5 Fabs bound were deposited to the Electron Microscopy Databank with the accession codes EMD-9144, EMD-9143, EMD-9145 EMD-9142, respectively. The cryo-EM map and fitted coordinates for H7 NY HA with 3 H7.7 Fabs bound has been deposited to the RCSB database with accession numbers EMD-9139/PDB 6MLM.
Funding: National Institutes of Health grant U19 AI117905 and National Institutes Health contract HHSN272201400024C. Advanced Photon Source, a US Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. The contents of this publication are solely the responsibility of the authors and do not necessarily represent the official views of NIAID, DOE, or NIH. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests: The authors have declared that no competing interests exist.
Abbreviations: bnAb, broadly neutralizing antibody; CDRH3, complementary determining region heavy chain 3; cryoEM, cryo-electron microscopy; Fab, fragment antigen binding; FSC, Fourier shell correlation; HA, hemagglutinin; HDX-MS, hydrogen–deuterium exchange mass spectrometry; H-FR3, heavy-chain framework region 3; mAb, monoclonal antibody; NA, neuraminidase; nsEM, negative-stain electron microscopy; PDB, Protein Data Bank; RBS, receptor-binding site; smFRET, single molecule Forster resonance energy transfer
Keywords: Influenza A; H7; Monoclonal antibodies.