Beyond DNA Binding: single C2H2 zinc fingers with adjacent β-strands mediate dimerization in Drosophila transcription factors

C2H2 proteins, characterized by DNA-binding C2H2-type zinc finger domains, constitute the largest group of transcription factors. In addition to binding DNA, C2H2 domains can mediate protein–protein interactions, facilitating oligomerization of C2H2 proteins. In this study, we identified eight C2H2 proteins in the Drosophila genome that feature a unique single C2H2 domain containing a conserved’CGEx’ motif. Yeast two-hybrid assays, SEC-MALS, and chemical cross-linking experiments revealed a strong propensity of these domains to form dimers. Using NMR spectroscopy, we determined the solution structure of the dimeric C2H2 domain from IMZF (Immune-mediated Zinc Finger) protein, providing structural evidence towards the dimerization of C2H2 domains. The structure revealed that dimerization is mediated by the interface between the core C2H2 fold and the adjacent β-strand containing’CGEx’ motif, which was further validated by structure-guided mutagenesis. A bioinformatic survey showed that’CGEx’-type C2H2 domains are specific to Diptera . Finally, we demonstrate that putatively dimerizing C2H2 domains containing additional structural elements beyond the canonical fold are widespread among diverse eukaryotic taxa, with the highest prevalence observed in insects. These findings establish that single C2H2 domains can mediate self-association and identify the’CGEx’-type C2H2 domain as a distinct structural subclass specific to Dipteran insects.