Cryo-EM reveals a double oligomeric ring scaffold of the CHIKV nsP3 peptide in complex with the NTF2L domain of host G3BP1.

Chikungunya virus (CHIKV) poses a severe threat to global public health. The interaction between CHIKV nsP3 and host G3BP1 is critical for viral replication. However, the exact structural mechanism of the nsP3-G3BP1 interaction is scarce. Here, we report a cryo-electron microscopy structure of an octameric-heterotrimer formed by CHIKV nsP3 peptide (designated as CHIKV-43) in complex with the nuclear translocation factor 2-like (NTF2L) domain of G3BP1. The overall structure presents a double-layer ring scaffold. Two FGDF motifs and two alpha helices of CHIKV-43 are essential to bind NTF2L. Particularly, the secondary alpha helix plays key roles in forming the CHIKV-43-NTF2L high-order oligomer. We next analyzed the detailed interactions between CHIKV-43 and the NTF2L domain. The different binding patterns of NTF2L with its various partners were described as well. Subsequently, we demonstrated that the CHIKV-43 peptide is a crucial factor for nsP3 co-localization with G3BP1, reducing stress granule formation and interfering with interferon production. Overall, our findings present the structural and functional mechanisms on CHIKV nsP3 modulating host G3BP1 and provide a potential antiviral target based on the protein-protein interaction interface. IMPORTANCE: Chikungunya virus (CHIKV) is an arbovirus responsible for causing fever, headache, and severe joint pain in humans, with widespread outbreaks affecting millions worldwide. The CHIKV nsP3 is a key protein that interacts with multiple host proteins. In this study, we present the cryo-electron microscopy structure of a high-order oligomer formed by the CHIKV nsP3 peptide and the nuclear translocation factor 2-like (NTF2L) domain of host protein G3BP1, revealing a completely novel interaction model. The detailed interactions within this oligomer were illustrated. We also analyzed the binding patterns of the NTF2L domain of G3BP1 with its various partners, providing essential insights for the development of peptide-mimetic inhibitors targeting nsP3 and/or G3BP1. Furthermore, our data indicate that the nsP3-G3BP1 interaction reduces stress granule formation and antagonizes interferon production. Overall, this study provides new knowledge on CHIKV biology and suggests a potential target for developing antiviral therapeutics.