Glucosylceramide is essential for Heartland and Dabie bandavirus glycoprotein-induced membrane fusion

Abstract

Due to climate changes, there has been a large expansion of emerging tick-borne zoonotic viruses, including Heartland bandavirus (HRTV) and Dabie bandavirus (DBV). As etiologic agents of hemorrhagic fever with high fatality, HRTV and DBV have been recognized as dangerous viral pathogens that likely cause future wide epidemics. Despite serious health concerns, the mechanisms underlying viral infection are largely unknown. HRTV and DBV Gn and Gc are viral surface glycoproteins required for early entry events during infection. Glycosphingolipids, including galactosylceramide (GalCer), glucosylceramide (GlcCer) and lactosylceramide (LacCer), are a class of membrane lipids that play essential roles in membrane structure and viral lifecycle. Here, our genome-wide CRISPR/Cas9 knockout screen identifies that glycosphingolipid biosynthesis pathway is essential for HRTV and DBV infection. The deficiency of UDP-glucose ceramide glucosyltransferase (UGCG) that produces GlcCer resulted in the loss of infectivity of recombinant viruses pseudotyped with HRTV or DBV Gn/Gc glycoproteins. Conversely, exogenous supplement of GlcCer, but not GalCer or LacCer, recovered viral entry of UGCG-deficient cells in a dose-dependent manner. Biophysical analyses showed that GlcCer targeted the lipid-head-group binding pocket of Gc to form a stable protein-lipid complex, which allowed the insertion of Gc protein into host lysosomal membrane lipid bilayers for viral fusion. Mutagenesis showed that D841 residue at the Gc lipid binding pocket was critical for GlcCer interaction and thereby, viral entry. These findings reveal detailed mechanism of GlcCer glycosphingolipid in HRTV and DBV Gc-mediated membrane fusion and provide a potential therapeutic target for tickborne virus infection.

SFTSV Gn‐Head mRNA vaccine confers efficient protection against lethal viral challenge

“…SFTSV infection progresses to symptoms such as fever, fatigue, myalgia, thrombocytopenia, leukopenia, multiorgan failure, and fatality up to 30% 1,3,4 . Structural analysis of the viral surface glycoproteins Gn and Gc, which cover the lipid bilayer envelope of SFTSV, has suggested their immunogenic targets for vaccine development 18,19 . Recent findings of NAbs in human convalescent sera have identified Gn as primary neutralizing epitopes 23,24 .…”

“…1,3,4 Structural analysis of the viral surface glycoproteins Gn and Gc, which cover the lipid bilayer envelope of SFTSV, has suggested their immunogenic targets for vaccine development. 18,19 Recent findings of NAbs in human convalescent sera have identified Gn as primary neutralizing epitopes. 23,24 Consistently, SFTSV Gn full-length 2,25 or its head region (sGn-H) 26 has demonstrated excellent vaccine candidates that induce potent antigenic and protective capacity.…”

“…17 The glycoproteins Gn and Gc, encoded by the M segment, are initially translated as a single precursor glycoprotein, and subsequently cleaved into Gn and Gc by cellular proteases. [18][19][20][21] The Gn and pre-fusion Gc form a heterodimer, anchoring themselves to the viral lipid bilayer envelope. 18,19 Structural analysis of the natural virion has revealed the presentation of SFTSV Gn, with its head region exposed to facilitate attachment to the host receptor CCR2.…”

“…It possesses a negative‐sense, single‐stranded, and tri‐segmented (L, M, and S) RNA genome 17 . The glycoproteins Gn and Gc, encoded by the M segment, are initially translated as a single precursor glycoprotein, and subsequently cleaved into Gn and Gc by cellular proteases 18–21 . The Gn and pre‐fusion Gc form a heterodimer, anchoring themselves to the viral lipid bilayer envelope 18,19 .…”

“…[18][19][20][21] The Gn and pre-fusion Gc form a heterodimer, anchoring themselves to the viral lipid bilayer envelope. 18,19 Structural analysis of the natural virion has revealed the presentation of SFTSV Gn, with its head region exposed to facilitate attachment to the host receptor CCR2. 22 Prior reports on neutralizing antibodies (NAbs) derived from convalescent human sera have also identified neutralization epitopes within the Gn head (Gn-H).…”