Furin cleavage of the SARS-CoV-2 spike is modulated by O-glycosylation.

The SARS-CoV-2 coronavirus responsible for the global pandemic contains a novel furin cleavage site in the spike protein (S) that increases viral infectivity and syncytia formation in cells. Here, we show that O-glycosylation near the furin cleavage site is mediated by members of the GALNT enzyme family, resulting in decreased furin cleavage and decreased syncytia formation. Moreover, we show that O-glycosylation is dependent on the novel proline at position 681 (P681). Mutations of P681 seen in the highly transmissible alpha and delta variants abrogate O-glycosylation, increase furin cleavage, and increase syncytia formation. Finally, we show that GALNT family members capable of glycosylating S are expressed in human respiratory cells that are targets for SARS-CoV-2 infection. Our results suggest that host O-glycosylation may influence viral infectivity/tropism by modulating furin cleavage of S and provide mechanistic insight into the role of the P681 mutations found in the highly transmissible alpha and delta variants.

O-glycosylation of the novel SARS-CoV-2 coronavirus spike protein influences furin cleavage

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is responsible for the pandemic that has affected millions of people worldwide. This virus contains a unique polybasic insertion (PRRA) within the spike protein, resulting in a novel furin cleavage site that has been shown to influence viral infectivity and syncytia formation in cell culture. This insertion also generates novel putative sites of O-glycosylation, a protein modification that has been shown in other proteins to influence furin cleavage. Here, we define the specific members of the UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferase (GALNT) family that are capable of glycosylating the novel SARS-CoV-2 coronavirus spike and examine their presence in human respiratory cells that are targets for SARS-CoV-2 infection. Moreover, we show that O-glycosylation by specific members of the GALNT enzyme family modulates furin cleavage of the spike in vivo. Given the well-established role of O-glycosylation in the regulation of proteolysis, our results suggest that O-glycosylation of SARS-CoV-2 may play roles in aspects of spike stability/processing, which may influence viral infectivity and tropism.