Interactions between the Nucleoprotein and the Phosphoprotein of Pneumoviruses: Structural Insight for Rational Design of Antivirals

Abstract

Pneumoviruses include pathogenic human and animal viruses, the most known and studied being the human respiratory syncytial virus (hRSV) and the metapneumovirus (hMPV), which are the major cause of severe acute respiratory tract illness in young children worldwide, and main pathogens infecting elderly and immune-compromised people. The transcription and replication of these viruses take place in specific cytoplasmic inclusions called inclusion bodies (IBs). These activities depend on viral polymerase L, associated with its cofactor phosphoprotein P, for the recognition of the viral RNA genome encapsidated by the nucleoprotein N, forming the nucleocapsid (NC). The polymerase activities rely on diverse transient protein-protein interactions orchestrated by P playing the hub role. Among these interactions, P interacts with the NC to recruit L to the genome. The P protein also plays the role of chaperone to maintain the neosynthesized N monomeric and RNA-free (called N0) before specific encapsidation of the viral genome and antigenome. This review aims at giving an overview of recent structural information obtained for hRSV and hMPV P, N, and more specifically for P-NC and N0-P complexes that pave the way for the rational design of new antivirals against those viruses.

Structural landscape of the Respiratory Syncytial Virus nucleocapsids

“…The helical NC, together with the RNA polymerase L, its phosphoprotein cofactor P and the transcription factor M2-1, form the RSV RNA synthesis complex that constitues the minimal infectious unit of the virus. P acts as a central hub by tethering L to the NC template, chaperoning neosynthesised N such as to keep it monomeric and RNA-free (N 0 ) for specific nascent RNA encapsidation, and recruiting M2-1 28 . The matrix protein M is thought to direct RSV assembly and budding by interacting both with the NC-bound P and with the envelope glycoprotein F 29,30 .…”

Molten globule driven and self-downmodulated phase separation of a viral factory scaffold

“…As in most nsNSVs Mononegavirales, the nucleocapsid of RSV is characterized by rod-shaped structures of helical symmetry with ten contiguous N protomers per turn forming a continuous groove that accommodates genomic RNA between the N- and C-terminal domains of the 391aa N protein (Figure 1A) [34, 35]. Similar to other Mononegavirales, recombinant expression of RSV N yields decameric ring-like structures wrapped by 70 nt long RNA molecules from the host cell (N RNA rings), where removal of RNA can only be achieved under strong chemical denaturation conditions and leads to irreversible aggregation of RNA free N (Figure 1B) [36-39].…”