Molecular rationale for hantavirus neutralization by a reservoir host-derived monoclonal antibody

Abstract

The intricate lattice of Gn and Gc glycoprotein spike complexes at the surface of hantaviruses facilitates host-cell entry and is the primary target of the neutralizing antibody-mediated immune response. Here, through study of a neutralizing monoclonal antibody (mAb 4G2) generated in a bank vole reservoir host following infection with Puumala virus (PUUV), we provide molecular-level insights into how antibody-mediated targeting of the hantaviral glycoprotein lattice effectively neutralizes the virus. Crystallographic analysis reveals that mAb 4G2 binds to a multi-domain site on Gc in the pre-fusion state, and that Fab binding is incompatible with the conformational changes of the Gc that are required for host cell entry.Cryo-electron microscopy of PUUV-like particles treated with Fab 4G2 demonstrates that the antibody binds to monomeric Gc at breaks in the Gn-Gc lattice, highlighting the immunological accessibility of Gc monomers on the mature hantavirus surface and the plastic nature of the higher-order lattice assembly. This work provides a structure-based blueprint for rationalizing antibody-mediated targeting of hantaviruses. IntroductionRodent-borne hantaviruses (genus Orthohantavirus, family Hantaviridae) are enveloped, negative-sense RNA viruses found worldwide in small mammals [1,2]. Cross-species transmission into humans typically results from inhalation of aerosolized excreta from chronically infected rodents, and has two primary clinical outcomes. Hantaviral species native to Europe and Asia cause hemorrhagic fever with renal syndrome (HFRS), while those in the Americas cause hantavirus cardiopulmonary syndrome (HCPS) [1,3,4]. The case mortality rate may exceed 30 % for HCPS and ranges from <1% to 15% for HFRS [2,5,6]. Despite variable clinical characteristics, both syndromes arise from excessive proinflammatory and cellular immune responses to infection [7,8]. Due to their potential to cause severe disease and to be transmitted by aerosols, hantaviruses have been identified as potential bioterrorism agents by the Centers for Disease Control and Prevention [9].Entry of a hantavirus into a host-cell is negotiated by two membrane-anchored glycoproteins, Gn and Gc, which form a lattice decorating the lipid bilayer envelope of the mature virion [10][11][12]. Gn and Gc are translated as a single polypeptide, and cleaved at a 'WAASA' signal sequence during protein folding and assembly [13,14]. Recent studies have reported crystal structures of both Gn [15,16] and Gc [17,18] ectodomains, and their higherorder, tetrameric organization has been postulated based upon biochemical characterization[10] and cryo-electron microscopy reconstructions of purified virions [11,12,16]. The Gn ectodomain exhibits a mixed α/β fold, which locates to the membrane-distal region of the tetrameric spike and is linked to the virion envelope by a C-terminal stalk region [11,15,16].The Gc adopts a three-domain (domains IIII) class II fusion protein architecture, and is postulated to associate closely with the Gn, linking adjacent G...

Naturally Acquired Rift Valley Fever Virus Neutralizing Antibodies Predominantly Target the Gn Glycoprotein

“…Our recombinantly derived RVFV Gn and Gc were secreted from HEK 293T cells and thus subject to the cellular folding checkpoints that exist in mammalian cells ( Ellgaard and Helenius, 2003 ). Similar constructs and protein production methods have been used to successfully produce and crystallize phleboviral Gn ( Halldorsson et al., 2018 ) and Gc glycoproteins ( Halldorsson et al, 2016 ), as well as the Gn and Gc from related hantaviruses ( Li et al, 2016 ; Rissanen et al, 2017 ; Rissanen et al., 2020 ), and their native-like fold architectures have been shown to be compatible with cryoEM-derived reconstructions of purified virions and virus-like particles ( Halldorsson et al., 2018 ). These combined observations indicate that our recombinantly produced RVFV proteins can serve as “native-like” mimetics of RVFV Gn and Gc.…”