We present evidence that the severe acute respiratory syndrome coronavirus (SARS) non-structural protein 13 (Nsp13) modulates the Z-RNA dependent regulated cell death pathway of necroptosis (1). We show that Z-prone sequences (called flipons (2)) exist in coronavirus and provide a signature that enables identification of the animal viruses which have become human pathogens. We also identify a potential RHIM in Nsp13. These two observations allow us to suggest a model in which Nsp13 may regulate Z-RNA-initiated RHIM-dependent cell death outcomes at two steps. The first step involves possible new ATP-independent Z-flipon helicase activity in Nsp13, which is distinct from the activity of the canonical A-RNA helicase. This activity unwinds/quenches nascent Z-RNAs, preventing their sensing by ZBP1. The second step involves RHIM-dependent inhibition of ZBP1, RIPK3 and/or RIPK1, preventing cell death downstream of Z-RNA sensing. Together the RHIM and Z-flipon helicase have the potential to alter the host response to the virus and the effectiveness of drugs targeting the NSP13 helicase.

We present evidence that the severe acute respiratory syndrome coronavirus (SARS) non-structural protein 13 (Nsp13) modulates the Z-RNA dependent regulated cell death pathway of necroptosis (1). We show that Z-prone sequences (called flipons (2)) exist in coronavirus and provide a signature that enables identification of the animal viruses which have become human pathogens. We also identify a potential RHIM in Nsp13. These two observations allow us to suggest a model in which Nsp13 may regulate Z-RNA-initiated RHIM-dependent cell death outcomes at two steps. The first step involves possible new ATP-independent Z-flipon helicase activity in Nsp13, which is distinct from the activity of the canonical A-RNA helicase. This activity unwinds/quenches nascent Z-RNAs, preventing their sensing by ZBP1. The second step involves RHIM-dependent inhibition of ZBP1, RIPK3 and/or RIPK1, preventing cell death downstream of Z-RNA sensing. Together the RHIM and Z-flipon helicase have the potential to alter the host response to the virus and the effectiveness of drugs targeting the NSP13 helicase.