Investigating the molecular mechanisms of membrane remodeling by coronaviruses

Coronaviruses are enveloped positive-sense RNA viruses. Over the last two decades, coronaviruses have led to severe respiratory infections in humans. Most recently, SARS-CoV-2 led to a global pandemic and resulted in more than 6.5 million deaths globally since December 2019. We currently lack a sufficiently broad set of antiviral drugs targeting different aspects of coronavirus replication. Therefore, developing new antiviral drugs targeting currently untargeted aspects of coronavirus replication may help reduce the mortality of future coronavirus infections. As such, it is critical to understand the molecular mechanisms of many different aspects of coronavirus replication as this will help to determine which aspects of viral replication may be useful targets for the development of new antiviral drugs. One aspect of coronavirus replication that is not well understood is the mechanisms by which coronaviruses remodel host cell membranes. Once coronaviruses infect host cells, a set of nonstructural proteins (nsps) are produced from the viral RNA. Three of these nsps, nsp3, nsp4 and nsp6, are integral membrane proteins that remodel host cell membranes to generate double-membrane vesicles (DMVs) from the endoplasmic reticulum (ER). These DMVs serve as the assembly sites for the replication and transcription complexes that are critical to producing viral RNA. In addition, DMVs have been shown to contain viral RNA further highlighting the critical role of DMVs in viral RNA production. While it is clear that membrane remodeling by coronaviruses is essential for their replication, we currently lack an understanding of the molecular mechanisms by which coronaviruses remodel host cell membranes to generate DMVs. One major reason for our limited understanding of this process, is that no studies have investigated the structure and function of the membrane-spanning regions of nsp3, nsp4 and nsp6 using purified proteins. As such, we will purify nsp3, nsp4 and nsp6 for structural studies using cryo-EM and for biochemical investigations using model membranes including liposomes and giant unilamellar vesicles. Importantly, this will work will not only provide new insight into the mechanisms of coronavirus replication, but it will also help reveal if membrane remodeling by coronaviruses may be a useful target for the development of future antiviral drugs.