Wilcox, X. E. | bioRxiv Science

bioRxiv2025

Structural Repertoire of HCV Broadly Neutralizing Antibodies Targeting the E2 Front Layer Supersite

Structural studies of the hepatitis C virus (HCV) E2 glycoprotein in complex with broadly neutralizing antibodies (bNAbs) have been instrumental in mapping neutralizing epitopes and guiding the rational design of immunogens. However, robust structural classification of HCV bNAbs is lacking, complicating immunogen design. The majority of HCV bNAbs recognize the E2 front layer (FRLY) supersite. Here, we developed a roadmap for the structural classification of FRLY-specific bNAbs. We discovered three distinct structural classes, each utilizing a unique binding mode to engage the FRLY supersite. HCV strains with multiple FRLY polymorphisms had a profound impact on binding and neutralization of bNAbs from distinct FRLY classes. Our findings establish the FRLY as a major antigenic supersite targeted by three bNAb classes and underscore the intrinsic structural plasticity of VH1-69-encoded HCV bNAbs.

immunology↗

bioRxiv2025

A miniature CRISPR-Cas10 enzyme confers immunity by an inverse signaling pathway

Microbial and viral co-evolution has created immunity mechanisms involving oligonucleotide signaling that share mechanistic features with human anti-viral systems1. In these pathways, including CBASS and type III CRISPR systems in bacteria and cGAS-STING in humans, oligonucleotide synthesis occurs upon detection of virus or foreign genetic material in the cell, triggering the antiviral response2-4. In a surprising inversion of this process, we show here that the CRISPR-related enzyme mCpol synthesizes cyclic oligonucleotides constitutively as part of an active mechanism that maintains cell health. Cell-based experiments demonstrated that the absence or loss of mCpol-produced cyclic oligonucleotides triggers cell death, preventing spread of viruses that attempt immune evasion by depleting host cyclic nucleotides. Structural and mechanistic investigation revealed mCpol to be a di-adenylate cyclase whose product, c-di-AMP, prevents toxic oligomerization of the effector protein 2TM{beta}. Analysis of cells by fluorescence microscopy showed that lack of mCpol allows 2TM{beta}-mediated cell death due to inner membrane collapse. These findings unveil a powerful new defense strategy against virus-mediated immune suppression, expanding our understanding of oligonucleotides in cell health and disease. These results raise the possibility of similar protective roles for cyclic oligonucleotides in other organisms including humans.

biochemistry↗