G3BP1

(Lu, Corbett NatCom 2021 PMID: 33479198) SARS-CoV-2 N condensates recruit the stress granule protein G3BP1.

The SARS-CoV-2 N protein has been reported to interact strongly with the stress granule core proteins G3BP1 and G3BP2 plus thousands of host mRNAs57,58,62,63, highlighting a potential relationship between N protein condensates and stress granules.

The colocalization of N with G3BP1 is even more obvious in cells expressing phosphorylation-resistant N14SA and NΔSR variant proteins, while the phospho-mimic mutant N11SD behaves similarly to wild-type protein (Fig. 6a).

We found that mRNAs are not enriched in the smaller condensates formed from wild-type N or the phospho-mimic N11SD mutant, but that mRNAs are highly enriched in the larger condensates formed from the N14SA and NΔSR mutants (Fig. 6c). We also observed mRNA localization to wild-type N protein condensates in cells treated with the kinase inhibitors kenpaullone and SRPIN340 (Supplementary Fig. 8).

Thus, the SARS-CoV-2 N protein forms RNA:protein condensates that recruit G3BP1, but not other stress granule proteins.

The morphology of N protein condensates in cells is similar to that of stress granules, cytoplasmic RNA:protein condensates that form in response to stress and sequester mRNAs34,59–61. Stress granules are thought to play a significant role in initiating the antiviral innate immune response77–84. Many viruses have been shown to specifically inhibit stress granule formation, often by directly binding the stress granule core protein G3BP1, as a means to evade the host innate immune response85–102. We find that SARS-CoV-2 N protein condensates recruit G3BP1, but not other known stress granule proteins, including UBAP2L, DDX1, and EIF3η. These findings parallel another recent report showing that SARS-CoV-2 N sequesters G3BP1 and G3BP2, inhibits the formation of stress granules in infected cells, and alters the transcriptional program of infected cells by binding and sequestering host mRNAs62. In addition, we determine that host mRNA localization to N protein condensates responds to N protein phosphorylation state, with enhanced localization to condensates of unphosphorylated N protein. Thus, in addition to its roles in viral transcription and RNA packaging, SARS-CoV-2 N likely plays a role in suppressing the host innate immune response by directly targeting, and sequestering G3BP1 and host mRNAs. The importance of these roles for viral replication and immune evasion, and the regulatory role of phosphorylation in modulating the diverse activities of the N protein, are important areas for future study.

PMID: 35240128 / 2022 / Biswal/Song : SARS-CoV-2 Nucleocapsid Protein Targets a Conserved Surface Groove of the NTF2-like Domain of G3BP1