Cap binding and immune evasion revealed by Lassa nucleoprotein structure

Abstract

Summary Lassa fever virus (LASV) causes thousands of deaths yearly and is a biological threat agent, for which there is no vaccine and limited therapy1. The nucleoprotein (NP) of LASV plays essential roles in viral RNA synthesis and immune suppression2-6, the molecular mechanisms of which are poorly understood. Here, we report the crystal structure of LASV NP at 1.80 Angstrom resolution, which reveals N- and C-domains with structures unlike any of the reported viral NPs7-10. The N domain folds into a novel structure with a deep cavity for binding the m7GpppN cap structure that is required for viral RNA transcription, whereas the C domain contains 3′-5′ exoribonuclease activity involved in suppressing interferon induction. This is the first X-ray crystal structure solved for an arenaviral NP, which reveals its unexpected functions and suggests unique mechanisms in cap binding and immune evasion. These findings provide great potential for vaccine and drug development.

Crimean–Congo hemorrhagic fever virus nucleoprotein reveals endonuclease activity in bunyaviruses

“…Interestingly, the paper by Qi and colleagues also reported that both trimeric and hexameric forms of LASV NP can degrade dsDNA, whereas they did not comment on which part of the LASV NP is responsible for this DNase activity (18). The similar enzymatic activity of the CCHFV and LASV nucleoproteins raises the possibility that the function of (−)ssRNA virus nucleoproteins is more complex than previously anticipated.…”

“…Qi and colleagues presented the first full-length LASV NP structure and proposed that the full-length LASV NP contains an RNA-specific 3′-5′ exonuclease activity (18). This exonuclease activity was confirmed by an independent group who located this function to the C-terminal domain (16).…”

“…Both CCHFV and LASV antagonize the host IFN response to infection by interfering with the activation pathway of IRF-3 (23). Further studies have suggested that, in LASV, the exoribonuclease activity encoded by the C-terminal domain of LASV NP is responsible for this suppression of innate immunity (16,18). However, results from IFN induction reporter assays driven by INF-β or IFN-stimulated response element (ISRE) promoters indicated that CCHFV NP did not induce a significant type I IFN response (Fig.…”

“…Previous structures of NPs from other families, such as the influenza virus (Orthomyxovidae) (11,12), rabies virus (Rhabdoviridae) (13), vesicular stomatitis virus (VSV) (Rhabdoviridae) (14), and borna disease virus (BDV) (Bornaviridae) (15) have shown how NPs assemble with RNA to form RNPs. Interestingly, recent studies by two research groups on the structure of the Lassa fever virus (LASV) (Arenaviridae) NP have added to our understanding of the functions of virally encoded NPs beyond their role in the packaging of viral genomic RNA (16)(17)(18). Both groups concur that the LASV C-terminal domain possesses 3′-5′ RNA-specific exoribonuclease activity, whereas they hold different opinions on the function of the N-terminal domain.…”

“…Both groups concur that the LASV C-terminal domain possesses 3′-5′ RNA-specific exoribonuclease activity, whereas they hold different opinions on the function of the N-terminal domain. Qi et al describe a LASV NP(1-569)-dTTP complex structure and propose that the LASV NP is responsible for the RNA cap-snatching mechanism that initiates its transcription (18). In contrast, Hastie and colleagues report the structure of a LASV(1-340)-ssRNA complex showing that the N-terminal domain possesses an RNA-binding crevice for the viral genome (17).…”