Ran modulates allosteric crosstalk between importin β surfaces

Area of Science:

• Molecular Biology
• Structural Biology
• Cell Biology

Background:

• Nuclear transport relies on the GTPase Ran gradient and importin β.
• Ran-GTP's precise role in modulating importin β activity during nuclear import is not fully understood.
• Importin β interacts with phenylalanine-glycine-rich nucleoporins (FG-nups) to facilitate cargo passage.

Purpose of the Study:

• To elucidate the structural mechanisms by which Ran-GTP modulates importin β activity.
• To characterize the conformational states of importin β in complex with key import/export factors.
• To correlate structural findings with biochemical data to understand nuclear import regulation.

Main Methods:

• Cryogenic electron microscopy (cryo-EM) single-particle analysis was used to determine structures.
• Five distinct conformational states of importin β with various effectors were resolved.
• Biochemical assays were performed to correlate structural data with functional activities.

Main Results:

• Ran-GTP, but not Ran-GDP, induces a constrained solenoid structure in importin β.
• This structural change closes high-affinity FG-binding pockets on importin β.
• Ran-GTP allosterically displaces import cargo by altering interactions between importin β surfaces.

Conclusions:

• Ran-GTP binding induces conformational changes in importin β, regulating its interaction with FG-nups and cargo release.
• An allosteric mechanism explains how Ran-GTP facilitates nuclear import and cargo dissociation.
• This proposed allosteric mechanism is likely applicable to other β-karyopherins involved in nuclear transport.