Hantaviruses use the endogenous host factor P58.sup.IPK to combat the PKR antiviral response

Hantavirus nucleocapsid protein (NP) inhibits protein kinase R (PKR) dimerization by an unknown mechanism to counteract its antiviral responses during virus infection. Here we demonstrate that NP exploits an endogenous PKR inhibitor P58.sup.IPK to inhibit PKR. The activity of P58.sup.IPK is normally restricted in cells by the formation of an inactive complex with its negative regulator Hsp40. On the other hand, PKR remains associated with the 40S ribosomal subunit, a unique strategic location that facilitates its free access to the downstream target eIF2[alpha]. Although both NP and Hsp40 bind to P58.sup.IPK, the binding affinity of NP is much stronger compared to Hsp40. P58.sup.IPK harbors an NP binding site, spanning to N-terminal TPR subdomains I and II. The Hsp40 binding site on P58.sup.IPK was mapped to the TPR subdomain II. The high affinity binding of NP to P58.sup.IPK and the overlap between NP and Hsp40 binding sites releases the P58.sup.IPK from its negative regulator by competitive inhibition. The NP-P58.sup.IPK complex is selectively recruited to the 40S ribosomal subunit by direct interaction between NP and the ribosomal protein S19 (RPS19), a structural component of the 40S ribosomal subunit. NP has distinct binding sites for P58.sup.IPK and RPS19, enabling it to serve as bridge between P58.sup.IPK and the 40S ribosomal subunit. NP mutants deficient in binding to either P58.sup.IPK or RPS19 fail to inhibit PKR, demonstrating that selective engagement of P58.sup.IPK to the 40S ribosomal subunit is required for PKR inhibition. Cells deficient in P58.sup.IPK mount a rapid PKR antiviral response and establish an antiviral state, observed by global translational shutdown and rapid decline in viral load. These studies reveal a novel viral strategy in which NP releases P58.sup.IPK from its negative regulator and selectively engages it on the 40S ribosomal subunit to promptly combat the PKR antiviral responses.