Crocodilepox Virus Protein 157 Is an Independently Evolved Inhibitor of Protein Kinase R

Area of Science:

• Virology
• Molecular Biology
• Evolutionary Biology

Background:

• Poxviruses, including Crocodilepox virus (CRV), often encode inhibitors targeting host protein kinase R (PKR).
• PKR activation by viral double-stranded RNA (dsRNA) halts viral replication by shutting down mRNA translation.
• CRV was previously thought to lack known PKR inhibitors, necessitating investigation of potential candidates.

Purpose of the Study:

• To experimentally characterize CRV157, a potential inhibitor of host PKR in Crocodilepox virus.
• To determine if CRV157 can inhibit PKR and rescue viral replication in a poxvirus infection model.
• To investigate the evolutionary origins and mechanisms of CRV157 as a PKR inhibitor.

Main Methods:

• Bioinformatic analyses to assess CRV157's evolutionary relationship to other poxviral PKR inhibitors.
• In vitro assays to confirm CRV157's dsRNA binding and PKR inhibition across species.
• Construction of recombinant vaccinia virus strains expressing wild-type or mutant CRV157 to assess impact on viral replication and eIF2α phosphorylation.

Main Results:

• CRV157 demonstrated dsRNA binding, cytosolic co-localization with PKR, and inhibition of PKR from multiple species.
• Bioinformatic analysis revealed CRV157 evolved independently from other known poxvirus PKR inhibitors.
• Recombinant vaccinia virus expressing functional CRV157 showed rescued viral replication, unlike the mutant lacking dsRNA binding; this correlated with eIF2α phosphorylation levels.

Conclusions:

• CRV157 functions as a potent inhibitor of host PKR, crucial for efficient poxvirus replication.
• The independent evolution of CRV157 exemplifies convergent evolution in the development of poxviral strategies to counteract host antiviral defenses.
• CRV157 represents a novel class of poxvirus PKR inhibitors with potential implications for understanding viral evolution and host-pathogen interactions.