DDX3X syndrome mutations lock DDX3X-RNA conformational states to drive persistent pathological condensation and neuronal death

ABSTRACT DDX3X is a highly conserved RNA helicase associated with RNA metabolism, translation initiation, and deciding cell fate choices. Spontaneous mutations in DDX3X cause a rare genetic human disorder called DDX3X syndrome, showing a spectrum of neurodevelopmental and intellectual abnormalities. How missense mutations in DDX3X lead to aberrant cellular functions and pathological consequences is unclear. Here, we demonstrate that specific DDX3X syndrome missense mutations induce the formation of persistent, solid-like DDX3X stress granules by structurally altering the conformation of the DDX3X-RNA complex. Structural interrogation of DDX3X syndrome missense mutations revealed critical mutations that perturb the DDX3X-RNA complex, exhibit high clinical pathogenicity scores, and are associated with cancers. N and C-terminal mutations adjacent to the helicase domain of the DDX3X (F182V, I190S, T198P, L556S, and L559H) showed augmented stress granule (SG) assembly, and formation of persistent DDX3X-SGs in neuronal and non-neuronal cells. Intriguingly, these mutations altered the liquid-like properties of DDX3X-SGs, forming solid-like SGs. Mechanistically, these mutations drive the persistent DDX3X-SGs by either locking DDX3X in an open, RNA-bound conformation or by increasing the rigidity of the DDX3X-RNA complex (I190S; T198P), thereby conferring a loss of liquid-like properties. The persistent solid-like DDX3X-SGs preferentially promoted neuronal lytic cell death and did not affect translation. Also, the C-terminal L556S and L559H mutations, which form persistent granules, promoted the DDX3X-driven β-amyloid aggregation. Our observations indicate that DDX3X syndrome mutations near the N- and C-termini promote the formation of solid-like DDX3X condensates, neuropathological aggregation, and neuronal cell death, which might underlie the disease pathogenesis in humans. GRAPHICAL ABSTRACT