Abstract
Many enveloped viruses are considered as medically important human pathogens and at present many of these viruses lack efficient antiviral treatments. The membranes of enveloped viruses contain embedded virus-encoded glycoproteins that are essential for viral infectivity, making them ideal antiviral drug targets. Enveloped viruses are known to exploit the host cell secretory pathway for the transportation of these glycoproteins to the site of viral envelopment. Prior to trafficking through the secretory pathway, the Sec61 translocon is hypothesized to mediate the translocation of these virus-encoded glycoproteins into the ER membrane. Here I utilise mycolactone, an exotoxin that has previously been identified as a potent Sec61 inhibitor, and has been shown to block the translocation of many secretory and transmembrane proteins, to assess the potential of the Sec61 translocon to act as a broad-spectrum antiviral drug target.
Ultimately, this project has demonstrated the ability of mycolactone to inhibit the production of infectious herpes simplex virus type 1 (HSV-1), zika virus (ZIKV), respiratory syncytial virus (RSV), influenza A virus (IAV) and severe acute respiratory coronavirus 2 (SARS-CoV-2) particles. I have also shown that the expression of a range of virus-encoded type I and II transmembrane proteins is dependent upon the Sec61 translocon, as the expression of these proteins was inhibited in mycolactone treated cells under non-viral and viral conditions. In addition, I have utilised in vitro translocation assays to show that the translocation of virus-encoded type I and II proteins is blocked in the presence of mycolactone, thus indicating that these viral proteins are translocated into the ER membrane via a Sec61-dependent mechanism. By contrast, mycolactone generally had little to no effect on the expression or translocation of a range of virus-encoded type III and polytopic proteins, thus indicating that these viral proteins are translocated into the ER membrane via a Sec61-independent mechanism. However, interestingly, the ZIKV and SARS-CoV-2 polyproteins were shown to have different susceptibilities to mycolactone. While mycolactone inhibited the expression of multiple components of the ZIKV polyprotein, it had no effect on SARS-CoV-2 genome replication, indicating that the SARS-CoV-2 polyprotein was still produced in the presence of mycolactone.