Novel Z-DNA binding domains in giant viruses

Z-nucleic acid structures play vital roles in cellular processes and have implications in innate immunity due to their recognition by Za a domains containing proteins (Z-DNA/Z-RNA binding proteins, ZBPs). Although Za a domains have been identified fi ed in six proteins, including viral E3L, ORF112, and I73R, as well as, cellular ADAR1, ZBP1, and PKZ, their prevalence across living organisms remains largely unexplored. In this study, we introduce a computational approach to predict Za a domains, leading to the revelation of previously unidentifi ed Za a domain-containing proteins in eukaryotic organisms, including non-metazoan species. Our fi ndings encompass the discovery of new ZBPs in previously unexplored giant viruses, members of the Nucleocytoviricota phylum. Through experimental validation, we confirm fi rm the Za a functionality of select proteins, establishing their capability to induce the B-to-Z conversion. Additionally, we identify Za-like a-like domains within bacterial proteins. While these domains share certain features with Za a domains, they lack the ability to bind to Z-nucleic acids or facilitate the B-to-Z DNA conversion. Our fi ndings significantly fi cantly expand the ZBP family across a wide spectrum of organisms and raise intriguing questions about the evolutionary origins of Za-containing a-containing proteins. Moreover, our study offers fresh perspectives on the functional significance fi cance of Za a domains in virus sensing and innate immunity and opens avenues for exploring hitherto undiscovered functions of ZBPs.