Structures of phlebovirus glycoprotein Gn and identification of a neutralizing antibody epitope

Abstract

Severe fever with thrombocytopenia syndrome virus (SFTSV) and Rift Valley fever virus (RVFV) are two arthropod-borne phleboviruses in the Bunyaviridae family, which cause severe illness in humans and animals. Glycoprotein N (Gn) is one of the envelope proteins on the virus surface and is a major antigenic component. Despite its importance for virus entry and fusion, the molecular features of the phleboviruse Gn were unknown. Here, we present the crystal structures of the Gn head domain from both SFTSV and RVFV, which display a similar compact triangular shape overall, while the three subdomains (domains I, II, and III) making up the Gn head display different arrangements. Ten cysteines in the Gn stem region are conserved among phleboviruses, four of which are responsible for Gn dimerization, as revealed in this study, and they are highly conserved for all members in Bunyaviridae. Therefore, we propose an anchoring mode on the viral surface. The complex structure of the SFTSV Gn head and human neutralizing antibody MAb 4-5 reveals that helices α6 in subdomain III is the key component for neutralization. Importantly, the structure indicates that domain III is an ideal region recognized by specific neutralizing antibodies, while domain II is probably recognized by broadly neutralizing antibodies. Collectively, Gn is a desirable vaccine target, and our data provide a molecular basis for the rational design of vaccines against the diseases caused by phleboviruses and a model for bunyavirus Gn embedding on the viral surface.bunyavirus | SFTSV | glycoprotein | neutralizing antibody | RVFV

An anti-Gn glycoprotein antibody from a convalescent patient potently inhibits the infection of severe fever with thrombocytopenia syndrome virus

“…In the stem region, replacing the cystine residues (C349, C356, C376, and C381) reduced the relative reactivity by more than 80%. This observation was consistent with a previous report that the structural stability of Gn was disrupted by a C356A mutation[29]. Also, mutation of the flanking residues of cystine, corresponding to G351, L354, E355, I357, T374, and V375 also reduced the reactivity by over 60%.…”

“…Thus far, MAb4-5 is the only human neutralizing monoclonal antibody reported, and it was developed using a combinatorial human antibody library from five patients[28]. MAb4-5 binds to domain III of SFTSV Gn glycoprotein[29]. The neutralizing effect of MAb4-5 has been shown only in in vitro , and its in vivo efficacy remains to be shown.…”

Vaccination with single plasmid DNA encoding IL-12 and antigens of severe fever with thrombocytopenia syndrome virus elicits complete protection in IFNAR knockout mice

“…While vaccination with either protein antigen failed to provide complete protection against lethal SFTSV challenge, Gc vaccine prolonged the survival time of infected mice and Gn antigen can provide partial protection. Considering that Gn and Gc glycoproteins function as viral ligands for cellular receptor binding and viral membrane fusion in host endosome, respectively [31][32][33], neutralization of both antigens might be required to completely block viral attachment and entry into host cells.…”

Vaccination with single plasmid DNA encoding IL-12 and antigens of severe fever with thrombocytopenia syndrome virus elicits complete protection in IFNAR knockout mice

“…While vaccination with either protein antigen failed to provide complete protection against lethal SFTSV challenge, Gc vaccine prolonged the survival time of infected mice and Gn antigen can provide partial protection. Considering that Gn and Gc glycoproteins function as viral ligands for cellular receptor binding and viral membrane fusion in host endosome, respectively [30-32], neutralization of both antigens might be required to completely block viral attachment and entry into host cells.…”