DDX3X is a Cl^--sensitive RNA helicase

Area of Science:

• Molecular Biology
• Neuroscience
• Biochemistry

Background:

• Chloride (Cl-) homeostasis is crucial for neurodevelopment and mature neuronal function.
• Disruptions in Cl- balance are linked to neurodevelopmental disorders.
• DDX3X, an RNA helicase involved in stress granule assembly, is associated with neurodevelopmental disorders.

Purpose of the Study:

• To investigate the role of chloride ions in regulating the function of the DDX3X protein.
• To explore how Cl- interaction affects DDX3X's ATPase and RNA helicase activities.
• To understand the impact of a specific DDX3X mutation (R326H) on Cl- sensitivity and neurodevelopmental disorder pathophysiology.

Main Methods:

• In vitro biochemical assays to assess Cl- interaction with DDX3X's helicase core.
• Enzyme activity assays (ATPase and RNA helicase) to measure the effect of Cl-.
• Biomolecular condensation assays to evaluate DDX3X's propensity for stress granule formation.
• Cellular studies using neuroblastoma cells to observe DDX3X localization and stress granule dynamics.
• Analysis of the R326H mutation's effect on Cl- binding and function.

Main Results:

• Chloride ions directly bind to the RNA binding region of the DDX3X helicase core.
• This interaction impairs DDX3X's ATPase and RNA helicase activities at physiological concentrations.
• Chloride binding disrupts DDX3X's propensity for biomolecular condensation in vitro.
• In neuroblastoma cells, Cl- efflux triggers the formation of large, persistent DDX3X stress granules.
• The R326H mutation disrupts the Cl- binding site, impairing Cl- sensitive functions.

Conclusions:

• Chloride ion binding is a key regulator of DDX3X protein function.
• The findings elucidate the molecular mechanisms underlying DDX3X's role in stress granule formation.
• This study provides critical insights into the pathophysiology of neurodevelopmental disorders linked to DDX3X mutations.