β-Coronavirus Nsp6 hijacks host ER translocation machineries into viral replication centers

Abstract

{beta}-coronaviruses evade host immune detection by replicating their genomes within double membrane vesicles (DMVs) derived from endoplasmic reticulum (ER) membranes. For example, SARS-CoV and CoV-2 encode three non-structural membrane proteins (Nsp 3, 4, and 6) which can remodel the ER to form DMVs. Here we test whether Nsps also function to recruit key host machineries required for viral replication and assembly within ER-derived DMVs. We use mouse hepatitis virus to study whether {beta}-coronavirus Nsps coordinate ER remodeling with host machinery recruitment. We demonstrate that Nsp6 generates Nsp6-remodeled ER domains that sequester host ER insertases including the Sec61 translocon, EMC, and GEL complexes. FRAP and FLIP experiments confirm that Nsp6 domains remain continuous with the ER and do not restrict membrane protein diffusion, except for those insertases that are sequestered there by Nsp6. Together, these data demonstrate a dual role for Nsp6 in remodeling ER membranes and sequestering host translocation machinery away from the general ER and into DMVs.