Zα and Zβ domains of ADAR1 and ZBP1 bind to G-quadruplexes with low micromolar affinity

While it is well established that the Zα domains of ADAR1 and ZBP1 proteins bind Z-form-prone nucleic acids (Z-NAs), it has also been shown that the Zα domain of ADAR1 binds DNA G-Quadruplexes (GQ). However, no binding partner of the structurally homologous Zβ domain of ADAR1 has been identified to date. Based on AlphaFold and molecular dynamics simulations, it has recently been suggested that the Zβ domain of ADAR1 targets its substrate by recognizing GQs. Here, we provide the first experimental evidence for Zβ domain binding to select G-quadruplex RNA and DNA in vitro , with structural specificity and low micromolar affinity. We also demonstrate that the Zα domains of ZBP1 bind to both DNA and RNA GQs with similar affinity. These findings extend the range of potential functional roles for these proteins and open new hypotheses for testing in cells.