Dual mode of DDX3X as an ATP-dependent RNA helicase and ATP-independent nucleic acid chaperone

Area of Science:

• Biochemistry
• Molecular Biology
• Genetics

Background:

• Human DDX3X, a DEAD-box RNA helicase, is implicated in RNA metabolism, cancer, viral infections, and neurodegenerative diseases.
• The precise targets and mechanisms of DDX3X action remain incompletely understood despite extensive research.

Purpose of the Study:

• To systematically characterize the biochemical activities and substrate specificity of human DDX3X.
• To elucidate the role of DDX3X's structural domains in its molecular functions.

Main Methods:

• Biochemical assays to assess RNA helicase and nucleic acid annealing activities.
• ATP hydrolysis assays.
• Truncation mutation analysis of DDX3X domains.

Main Results:

• DDX3X functions as a bidirectional ATP-dependent RNA helicase, unwinding RNA duplexes and RNA-DNA hybrids.
• DDX3X exhibits nucleic acid annealing activity, particularly for DNA.
• DDX3X acts as an ATP-independent nucleic acid chaperone, destabilizing and stabilizing nucleic acid structures.
• The disordered N-terminal and C-terminal tails of DDX3X are essential for its biochemical activities, with the N-tail being particularly critical.

Conclusions:

• DDX3X possesses diverse biochemical activities including RNA unwinding, nucleic acid annealing, and chaperoning.
• The N- and C-terminal regions are vital for DDX3X's function, highlighting their importance in regulating its molecular mechanisms.
• These findings enhance understanding of DDX3X's role in RNA metabolism and DNA repair, with implications for developing DDX3X-targeted antiviral and anticancer therapies.