A genome-wide CRISPR-Cas9 screen reveals the requirement of host cell sulfation for Schmallenberg virus infection

Schmallenberg virus (SBV) is an insect-transmitted Orthobunyavirus that can cause abortions and congenital malformations in the offspring of ruminants. Even though the two viral surface glycoproteins Gn and Gc are involved in host cell entry, the specific cellular receptors of SBV are currently unknown. Using a genome-wide CRISPR-Cas9 forward screening, we identified 3′-phosphoadenosine 5′-phosphosulfate (PAPS) transporter 1 (PAPST1) as an essential factor for SBV infection. PAPST1 is a sulfotransferase involved in heparan sulfate proteoglycan synthesis encoded by solute carrier family 35 member B2 (SLC35B2). SBV cell surface attachment and entry were largely reduced upon knockout of SLC35B2, whereas reconstitution of SLC35B2 in these cells fully restores their susceptibility to SBV infection. Furthermore, treatment of cells with heparinase diminished infection with SBV, confirming that heparan sulfate plays an important role for cell attachment and entry. Although to varying degrees, heparan sulfate was also found to be important to initiate infection by two other Bunyaviruses, La Crosse and Rift Valley fever virus. Thus, PAPST1-triggered synthesis of cell surface heparan sulfate is required for efficient replication of SBV and other Bunyaviruses.