ZBP1 condensate formation synergizes Z-NAs recognition and signal transduction.

Z-DNA binding protein 1 (ZBP1) is a crucial player in the intracellular recognition of Z-form nucleic acids (Z-NAs) through its Zαß domain, initiating downstream interactions with RIPK1 and RIPK3 via RHIM domains. This engagement leads to the assembly of PANoptosomes, ultimately inducing programmed cell death to curb pathogen dissemination. How Zαß and RHIM domain cooperate to trigger Z-NAs recognition and signal transduction remains unclear. Here, we show that ZBP1 condensate formation facilitates Z-NAs binding and antiviral signal transduction. The ZBP1 Zαß dimerizes in a concentration-dependent manner, forming characteristic condensates in solutions evidenced by DLS and SAXS methods. ZBP1 exhibits a binding preference for 10-bp length CG (10CG) DNA and Z-RNA ligand, which in turn enhanced Zαß dimerization, expediting the formation of droplet condensates in vitro and amyloid-like puncta in cells. Subsequent investigations reveal that Zαß could form condensates with liquid-liquid phase separation property upon HSV and IAV infections, while full-length ZBP1 forms amyloid-like puncta with or without infections. Furthermore, ZBP1 RHIM domains show typical amyloidal fibril characterizations and cross-polymerize with RIPK1 depending on the core motif of 206IQIG209, while mutated ZBP1 could impede necroptosis and antiviral immunity in HT-29 cells. Thus, ZBP1 condensate formation facilitates the recognition of viral Z-NAs and activation of downstream signal transduction via synergic action of different domains, revealing its elaborated mechanism in innate immunity.

Formation of left-handed helices by C2'-fluorinated nucleic acids under physiological salt conditions.

Recent findings in cell biology have rekindled interest in Z-DNA, the left-handed helical form of DNA. We report here that two minimally modified nucleosides, 2'F-araC and 2'F-riboG, induce the formation of the Z-form under low ionic strength. We show that oligomers entirely made of these two nucleosides exclusively produce left-handed duplexes that bind to the Zα domain of ADAR1. The effect of the two nucleotides is so dramatic that Z-form duplexes are the only species observed in 10 mM sodium phosphate buffer and neutral pH, and no B-form is observed at any temperature. Hence, in contrast to other studies reporting formation of Z/B-form equilibria by a preference for purine glycosidic angles in syn, our NMR and computational work revealed that sequential 2'F…H2N and intramolecular 3'H…N3' interactions stabilize the left-handed helix. The equilibrium between B- and Z- forms is slow in the 19F NMR time scale (≥ms), and each conformation exhibited unprecedented chemical shift differences in the 19F signals. This observation led to a reliable estimation of the relative population of B and Z species and enabled us to monitor B-Z transitions under different conditions. The unique features of 2'F-modified DNA should thus be a valuable addition to existing techniques for specific detection of new Z-binding proteins and ligands.

Manipulating Radiation-Sensitive Z-DNA Conformation for Enhanced Radiotherapy.

DNA double-strand breaks (DSBs) yield highly determines radiotherapy efficacy. However, improving the inherent radiosensitivity of tumor DNA to promote radiation-induced DSBs remains a challenge. Using theoretical and experimental models, the underexplored impact of Z-DNA conformations on radiosensitivity, yielding higher DSBs than other DNA conformations, is discovered. Thereout, a radiosensitization strategy focused on inducing Z-DNA conformation, utilizing CBL@HfO2 nanocapsules loaded with a Z-DNA inducer CBL0137, is proposed. A hollow mesoporous HfO2 (HM-HfO2) acts as a delivery and an energy depositor to promote Z-DNA breakage. The nanocapsule permits the smart DSBs accelerator that triggers its radiosensitization with irradiation stimulation. Impressively, the CBL@HfO2 facilitates the B-Z DNA conformational transition, augmenting DSBs about threefold stronger than irradiation alone, generating significant tumor suppression with a 30% cure rate. The approach enables DSBs augmentation by improving the inherent radiosensitivity of DNA. As such, it opens up an era of Z-DNA conformation manipulation in radiotherapy.

Zeta potential of Z-DNA: A new signature to study B-Z transition in linear and branched DNA.

Zeta potential is commonly referred as surface charge density and is a key factor in modulating the structural and functional properties of nucleic acids. Although the negative charge density of B-DNA is well understood, there is no prior description of the zeta potential measurement of Z-DNA. In this study, for the first time we discover the zeta potential difference between B-DNA and lanthanum chloride-induced Z-DNA. A series of linear repeat i.e. (CG)n and (GC)n DNA as well as branched DNA (bDNA) structures was used for the B-to-Z DNA transition. Herein, the positive zeta potential of Z-DNA has been demonstrated as a powerful tool to discriminate between B-form and Z-form of DNA. The generality of the approach has been validated both in linear and bDNA nanostructures. Thus, we suggest zeta potential can be used as an ideal signature for the left-handed Z-DNA.

AIRE relies on Z-DNA to flag gene targets for thymic T cell tolerization.

AIRE is an unconventional transcription factor that enhances the expression of thousands of genes in medullary thymic epithelial cells and promotes clonal deletion or phenotypic diversion of self-reactive T cells1-4. The biological logic of AIRE's target specificity remains largely unclear as, in contrast to many transcription factors, it does not bind to a particular DNA sequence motif. Here we implemented two orthogonal approaches to investigate AIRE's cis-regulatory mechanisms: construction of a convolutional neural network and leveraging natural genetic variation through analysis of F1 hybrid mice5. Both approaches nominated Z-DNA and NFE2-MAF as putative positive influences on AIRE's target choices. Genome-wide mapping studies revealed that Z-DNA-forming and NFE2L2-binding motifs were positively associated with the inherent ability of a gene's promoter to generate DNA double-stranded breaks, and promoters showing strong double-stranded break generation were more likely to enter a poised state with accessible chromatin and already-assembled transcriptional machinery. Consequently, AIRE preferentially targets genes with poised promoters. We propose a model in which Z-DNA anchors the AIRE-mediated transcriptional program by enhancing double-stranded break generation and promoter poising. Beyond resolving a long-standing mechanistic conundrum, these findings suggest routes for manipulating T cell tolerance.