Scientists Reveal How the Monkeypox Virus Replicates

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"At a glance

• Study reveals how shape changes during the assembly of viral proteins switch on replication in monkeypox virus.
• The findings provide a foundation for understanding the molecular machines that drive infection in mpox and aiding the search for therapies.

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Although vaccines are available to help prevent mpox — the disease caused by the monkeypox virus — and its close relative smallpox, there is currently no antiviral that has been shown to be effective against mpox. ...

learning how two key proteins work together to allow monkeypox to replicate itself — the helicase-primase and the polymerase. Each member of the duo performs a distinct task. The helicase-primase unzips the virus’s DNA double helix and attaches a chemical anchor that allows a new strand of DNA to be built, and the polymerase recruits and organizes the building blocks that assemble into a new strand of DNA. Together these pieces are called the replisome. ...

In this study, the tweezers revealed the moment when the replisome began to unwind the DNA double helix. As hypothesized, when the team added the polymerase to the helicase-primase complex, the fully formed replisome began working. ..."

From the abstract:

"Poxviruses are double-stranded DNA viruses with large genomes. Among them, monkeypox virus (MPXV) has been responsible for two recent public health emergencies as declared by the World Health Organization.

The MPXV polymerase comprises three subunits—a catalytic subunit (F8) and a heterodimeric processivity factor (A22 and E4).

The viral polymerase must coordinate activities with the hexameric helicase–primase (E5) to initiate replication of the viral genome. Although structures of MPXV E5 and the polymerase in isolation are available, how they assemble into a functional replisome remains unclear.

In isolation, E5 is in an autoinhibited conformation and has very weak helicase activity, and the mechanism for helicase activation is unclear.

Here we used cryo-electron microscopy to determine the structures of DNA-bound MPXV replisomes comprising the polymerase holoenzyme (F8, A22 and E4) and the E5 helicase hexamer.

We show that, during replisome assembly, E5 undergoes large-scale conformational changes that allow two of its primase domains to interact with the polymerase F8 thumb and A22 subunit.

Biochemical assays and single-molecule experiments reveal that this E5 conformational change is coupled to helicase activation and enhances primase activity.

Taken together, these findings identify fundamental mechanisms governing coordinated helicase and polymerase activities during DNA replication for an important class of viral pathogens."

Scientists Reveal How the Monkeypox Virus Replicates | Harvard Medical School "Findings deepen understanding of what drives infection, could inform new therapies"

Structure and operating principles of a monkeypox virus replisome (open access)

Fig. 1: Cryo-EM structure of the MPXV replisome.

Fig. 2: Polymerase binding activates the E5 helicase.

Fig. 4: Structure of an MPXV polymerase–primase core complex and RNA-to-DNA elongation transitions.