MODULATION OF DDX3X ENZYMATIC FUNCTIONS BY DIVALENT CATIONS

Protein regulation by ions is a common biochemical mechanism that occurs in cells to maintain homeostasis, influencing protein function and interactions with other biomolecules. However, the bioaccumulation of certain metal ions can lead to disruption of protein functions. In fact, the imbalance of metal ions is a critical hallmark of several neurodegenerative diseases including Alzheimer disease, Parkinson disease, and prion disease. In this study, we investigated the effect of several divalent cations on the function of the neurodevelopmental protein DDX3X, an ATP-dependent RNA helicase member of the DEAD-box superfamily. DDX3X has important roles in nucleic acid metabolism and is involved in stress granule formation through liquid-liquid phase separation (LLPS). Like other DEAD-box helicases, DDX3X requires Mg(II) ions to enable ATP binding and hydrolysis. This activity depends on the interaction of Mg(II) and ATP with conserved regions (i.e. Motif I, Motif II, and the Q-motif). We found that DDX3X ATPase activity is significantly altered in the presence of Zn(II), Cd(II), Co(II), Ni(II), or Pd(II) ions. Moreover, Zn(II), Cd(II), Cu(II) or Pd(II) ions impaired DDX3X RNA helicase activity even at low concentrations. Furthermore, although LLPS occurred in all metal ion-treated samples, Zn(II) and Cd(II) ions induced noticeable morphological changes in DDX3X-rich droplets. Future studies will elucidate the structural mechanisms underlying metal-induced inhibition of DDX3X. Moreover, investigating the impact of metal ions on the RNA helicase function and phase separation in cellular contexts will be critical to fully understand the physiological relevance and potential pathological consequences of these findings.

This work was supported by the Brazilian Center for Research in Energy and Materials (CNPEM), a non-profit organization under the supervision of the Brazilian Ministry for Science, Technology, and Innovations (MCTI), and the National Council for Scientific and Technological Development (CNPq# 407904/2023-9).