Nipah virus matrix protein utilizes cortical actin to stabilize the virus assembly sites and promote budding

Several families of enveloped viruses assemble and bud from the host cell plasma membranes (PM), including paramyxoviruses. Nipah virus (NiV) is a deadly zoonotic paramyxovirus causing yearly outbreaks in Southeast Asia with >75% mortality. NiV encodes matrix proteins (M) that drive assembly and budding. NiV-M forms dimers and interacts with membrane lipids in the host cells PM for budding. Using single-molecule localization microscopy and single-particle tracking, we show that the host F-actin maintains the nanoscale organization of NiV assembly sites at the PM. This F-actin-dependent integrity of NiV assembly sites is observed at the membrane retention stage after the assembly process is complete, rather than during the recruitment of NiV-M molecules to these sites. NiV-M interacts with actin via its C-terminal domain. We also show that the actin-branching factor, Arp2/3 complex, promotes virus-like-particle production. Meanwhile, inhibiting Arp2/3 disfavors the PM retention of NiV assembly sites and NiV-M-mediated generation of membrane protrusions, but does not affect the assembly rate. This suggests that Arp2/3-nucleated actin polymerization and branching are critical for maintaining NiV-M assembly sites at the PM, allowing it to facilitate membrane protrusion generation for virus budding. Our findings support the following model: NiV-M interacts with F-actin through its C-terminus to remain at the host PM after assembly completion. This F-actin-dependent retention is promoted by the Arp2/3-driven actin branching and polymerization, which also drives the formation of NiV-M-induced membrane protrusions necessary for virus budding. SignificanceNipah virus (NiV) is a deadly paramyxovirus capable of animal-animal and animal-human transmissions. To produce a NiV particle, the NiV matrix protein (M) must create an assembly site by binding to the surface of an infected cell and pushing the cell membrane outward for virus budding. To do so, the NiV matrix protein must co-opt or overcome an actin network underneath the cell membrane. We provide single-molecule evidence that M interacts with the actin cytoskeleton for membrane retention but not recruitment of M to existing assembly sites. This process is promoted by the Arp2/3-driven actin branching and polymerization. Our findings suggest the role of actin remodeling in NiV budding and identify a druggable site at the C-terminus of NiV-M.