Researchers at Sanford Burnham Prebys have discovered the intricate machinery behind the Zika virus and a potential weakness that could be targeted for therapy. Published in PLOS Pathogens, the study reveals how Zika virus utilizes its limited genetic material and proteins to replicate and infect cells. The research team identified a multipurpose enzyme, NS2B-NS3, which acts as both a protease and a helicase in the virus.
According to Alexey Terskikh, the senior author of the study, the shape of the NS2B-NS3 enzyme complex determines its function. In the closed conformation, it acts as a protease, breaking up proteins. However, it can shift between open and super-open conformations, allowing it to grab and release single strands of RNA, which are essential for viral replication.
Zika virus is a type of RNA virus belonging to the flavivirus family, which includes other deadly pathogens such as dengue fever, yellow fever, and West Nile virus. Transmitted by mosquitoes, Zika virus is particularly dangerous for pregnant women as it infects uterine and placental cells. Once inside host cells, the virus reprograms them to produce more Zika virus.
Understanding the molecular mechanism of Zika virus could lead to the development of targeted therapies. While targeting the specific domains of the NS2B-NS3 enzyme for protease or helicase functions would be challenging due to similar molecules in human cells, blocking the shape-shifting ability of the enzyme complex could be an effective strategy. If the complex cannot transition between different conformations, it cannot perform its essential functions, thereby preventing the production of new Zika virus particles.
Previous studies have identified NS2B-NS3 as the essential enzyme in Zika virus, composed of NS2B-NS3pro and NS3hel units. NS2B-NS3pro acts as a protease, cutting long polypeptides into Zika proteins. However, the enzyme’s ability to bind single-stranded RNA and aid in the separation of double-stranded RNA during viral replication was only recently discovered.
Using crystal structures, protein biochemistry, fluorescence polarization, and computer modeling, the researchers examined the life cycle of NS2B-NS3pro. They found that when the complex is closed, NS3pro is connected to NS3hel through a short amino acid linker and is active as a protease. When the complex is open, RNA binding occurs, and the super-open conformation is required for RNA release.
The conformational changes in the enzyme complex are driven by the dynamics of NS3hel, which extends the linker and pulls NS3pro to release RNA. NS3pro is anchored to the endoplasmic reticulum (ER) of host cells—a crucial organelle responsible for protein transportation—via NS2B. While in the closed conformation, NS3pro cleaves the Zika polypeptide, facilitating the production of viral proteins.
On the other side of the linker, NS3hel separates the double-stranded RNA of Zika virus and transfers one strand to NS3pro, which has positively charged forks that attract the negatively charged RNA. The complex transitions into the closed conformation, releasing the RNA.
As NS3hel grabs the double-stranded RNA, the complex is pulled forward. However, due to the anchoring of NS3pro in the ER membrane and the limited extension of the linker, the complex shifts into the super-open conformation, releasing the RNA. The complex then returns to the open conformation, ready for the next cycle.
In addition to potentially providing a therapeutic target for Zika virus, this detailed understanding of the NS2B-NS3 enzyme complex could be applied to other flaviviruses that share similar molecular machinery.
Terskikh suggests that the NS2B-NS3pro complex found in different flaviviruses could be a new class of drug targets for multiple viruses. With further research, these findings could pave the way for the development of antiviral treatments not only for Zika virus but also for other related diseases.
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1. Source: Coherent Market Insights, Public sources, Desk research
2. We have leveraged AI tools to mine information and compile it
