# Monkeypox virus protein OPG188 antagonizes cGAS–STING antiviral signaling pathway to mediate immune evasion

## TL;DR

This study reveals how monkeypox virus evades the immune system by using a protein called OPG188 to block a key antiviral pathway and identifies potential treatments to counter this.

## Contribution

The study identifies OPG188 as a nuclease that degrades 2′3′-cGAMP and discovers two small molecules that inhibit its activity.

## Key findings

- OPG188's N-terminal domain cleaves the immune signaling molecule 2′3′-cGAMP.
- Four key residues in Poxin (H15, K140, R182, I79) are essential for its immune evasion function.
- NAD+ and Theaflavin-3’-gallate inhibit Poxin activity, restoring antiviral signaling.

## Abstract

This study identifies key monkeypox virus (MPXV) immune evasion proteins—OPG147, OPG188, and OPG200—that suppress the host cGAS–STING antiviral pathway. We characterize OPG188 as a nuclease that degrades the immune signaling molecule 2′3′-cGAMP and define critical functional residues via mutagenesis. Using structure-based screening, we find two small molecules (NAD+, Theaflavin-3’-gallate) that block Poxin activity, restoring antiviral signaling and highlighting their potential as therapeutics against MPXV infection. These findings provide crucial insights into poxvirus immune evasion and open avenues for developing virus-directed antiviral strategies.

Innate immune evasion is critical for productive viral replication. Activation of the cGAS–STING antiviral signaling pathway and its downstream effector genes plays a pivotal role in restricting viral replication during early DNA virus infection. Through a comprehensive genomic screen of monkeypox virus (MPXV), we identified three viral genes, OPG147, OPG188, and OPG200, whose expression potently suppresses cGAS–STING pathway activation. Notably, the N-terminal domain of the Poxin protein encoded by OPG188 exhibits nuclease activity and cleaves the cyclic dinucleotide second messenger 2′3′-cGAMP. Using site-directed mutagenesis, we further delineated nine conserved regions and four key amino acid residues—H15, K140, R182, and I79—within Poxin that are essential for antagonism of cGAS–STING signaling. Moreover, via molecular docking and high-throughput screening of 7,155 small molecules targeting the catalytic pocket of Poxin, we identified two compounds that competitively bind to Poxin, inhibiting its cGAMP—degrading activity and consequently restoring cGAS–STING-mediated antiviral signaling upon MPXV infection. Collectively, these findings underscore the pivotal role of OPG188 in modulating antiviral immune responses and highlight NAD+ and Theaflavin-3’-gallate as promising candidates for the development of anti-MPXV therapeutics.