Proteolytic processing of the Marburg virus glycoprotein depends on Sec616β and is required for cell entry
Ebola and Marburg virus (EBOV, MARV) cause severe disease and therapeutic options are urgently needed. The Sec61 translocon facilitates ER import of viral glycoproteins (GPs) and may represent a therapeutic target. Here, we report that the Sec61 subunit Sec61{beta}, although dispensable for GP expression, is required for proteolytic cleavage of MARV- but not EBOV-GP and that an intact furin motif is essential for robust cell entry of Marburg- but not Ebolaviruses. Further, MARV- but not EBOV-GP was cleaved by the furin-related enzyme SKI-1, for which a cleavage motif was identified in silico, and cleavage by SKI-1 was impaired in SEC61B-KO cells. In addition, Sec61{beta} was required for normal N-glycosylation of MARV-GP and mutation of a sequon (N563D) abrogated cleavage. Finally, the absence of Sec61{beta} modestly, and blockade of Sec61 via apratoxin S4 markedly, inhibited EBOV and MARV infection. These results reveal a differential protease dependence of MARV and EBOV and identify Sec61 as a potential therapeutic target. Author summaryThe filoviruses Ebola virus (EBOV) and Marburg virus (MARV) spread from animals to humans and can cause deadly outbreaks. These viruses rely on a surface glycoprotein (GP) for infection, which is processed by the enzyme furin in infected human cells. Cleavage of EBOV-GP was thought to be non-essential for infection. However, using lab models for filovirus entry into cells, we discovered that MARV, unlike EBOV, needs this cleavage step to infect cells efficiently. We also found that the host cell protein Sec61{beta} is necessary for proteolytic processing and glycosylation of MARV-GP but not EBOV-GP. In addition, we showed that another cellular enzyme, SKI-1, can process MARV- but not EBOV-GP. Finally, we found that removing Sec61{beta} or blocking Sec61 activity reduced infection by both viruses. These findings show key differences in how the two viruses interact with host cells and suggest that targeting Sec61 could be a promising new strategy to fight Ebola and Marburg virus infections.