Membrane rearrangements mediated by coronavirus nonstructural proteins 3 and 4

Coronaviruses replicate their genomes in association with rearranged cellular membranes. The coronavirus nonstructural integral membrane proteins (nsps) 3, 4 and 6, are key players in the formation of the rearranged membranes. Previously, we demonstrated that nsp3 and nsp4 interact and that their co-expression results in the relocalization of these proteins from the endoplasmic reticulum (ER) into discrete perinuclear foci. We now show that these foci correspond to areas of rearranged ER-derived membranes, which display increased membrane curvature. These structures, which were able to recruit other nsps, were only detected when nsp3 and nsp4 were derived from the same coronavirus species. We propose, based on the analysis of a large number of nsp3 and nsp4 mutants, that interaction between the large luminal loops of these proteins drives the formation of membrane rearrangements, onto which the coronavirus replication–transcription complexes assemble in infected cells.