The Sigma1 ER membrane receptor promotes structural protein folding and genome packaging of dengue virus.

Dengue virus (DENV) exploits the host endoplasmic reticulum (ER) to support viral protein translation and folding, replication, and assembly, although the identity of ER factors that promote these distinct steps during infection remain unclear. Here we demonstrate that the ER-resident Sigma1 ER membrane receptor (S1R) promotes virus structural protein folding and genome packaging of DENV during infection. Under S1R knockdown (KD), DENV infection is impaired without compromising virus translation or replication. Strikingly, EM analysis revealed that DENV particles in and secreted from S1R-depleted cells are smaller, likely because they are empty particles devoid of the vRNA genome. Biochemical experiments demonstrated that S1R binds to the prM structural protein and under S1R KD, the prM, E and C structural proteins became detergent-insoluble. Thus, without S1R, all three virus structural proteins misfold, impairing efficient genome packaging. Together, these findings identify a novel ER chaperone that supports a critical DENV infection step.