Poly(ADP-ribose) potentiates ZAP antiviral activity

Zinc-finger antiviral protein (ZAP), also known as poly(ADP-ribose) polymerase 13 (PARP13), is an antiviral factor that selectively targets viral RNA for degradation. ZAP is active against both DNA and RNA viruses, including important human pathogens such as hepatitis B virus and type 1 human immunodeficiency virus (HIV-1). ZAP selectively binds CpG dinucleotides through its N-terminal RNA-binding domain, which consists of four zinc fingers. ZAP also contains a central region that consists of a fifth zinc finger and two WWE domains. Through structural and biochemical studies, we found that the fifth zinc finger and tandem WWEs of ZAP combine into a single integrated domain that binds to poly(ADP-ribose) (PAR), a cellular polynucleotide. PAR binding is mediated by the second WWE module of ZAP and likely involves specific recognition of an adenosine diphosphate-containing unit of PAR. Mutation of the PAR binding site in ZAP abrogates the interaction in vitro and diminishes ZAP activity against a CpG-rich HIV-1 reporter virus and murine leukemia virus. In cells, PAR facilitates formation of non-membranous sub-cellular compartments such as DNA repair foci, spindle poles and cytosolic RNA stress granules. Our results suggest that ZAP-mediated viral mRNA degradation is facilitated by PAR, and provides a biophysical rationale for the reported association of ZAP with RNA stress granules. Author summary Zinc-finger antiviral protein (ZAP), also known as poly(ADP-ribose) polymerase 13 (PARP13), functions as a host defense mechanism against viruses, including important human pathogens such as hepatitis B virus and type 1 human immunodeficiency virus (HIV-1). ZAP recognizes and binds viral RNA by virtue of their nucleotide composition and directs selective degradation of these viral RNA. Here, we report the X-ray crystal structures of ZAP's central domain, which we found to bind poly(ADP-ribose) (PAR), a cellular polynucleotide. In cells, PAR is associated with macromolecular assemblages that are implicated in virus inhibition and antiviral signaling. We confirm through biochemical experiments that ZAP indeed binds PAR, both in vitro and in cells. However, the PAR-binding activity of ZAP is not essential to its antiviral function. Instead, we find that PAR binding is an ancillary activity that contributes to the potency of ZAP-mediated virus inhibition.

Automated summary

Zinc-finger antiviral protein (ZAP) is an antiviral factor that selectively degrades viral RNA. It has been found that ZAP binds to the cellular polynucleotide poly(ADP-ribose) (PAR), which facilitates ZAP-mediated viral mRNA degradation and is associated with RNA stress granules.