Eksport jądrowy

Nuclear export involves recognizing nuclear export signals or NES on the cargo protein.

NES are of three types: The classical 10-residue leucine-rich signal, a 38-residue M9 signal, and a 24-residue KNS signal.

NES are recognized by specialized nuclear transport receptors that shuttle the cargo through the nuclear pore complexes, or the NPC, on the nuclear membrane. Protein transport across the nucleus depends on the receptor binding to the small GTPase, Ran.

Protein exporting receptor— exportin 1 forms a complex with Ran-GTP and undergoes a conformational change. Exportin-Ran-GTP then binds the cargo to form a three-member complex.

The exportin-Ran-GTP-cargo complex shuttles through the NPC by interacting with the FG repeats on its inner lining and disrupts the gel-like selective barrier of the NPC to diffuse into the cytosol.

A GTPase activating protein called Ran-GAP present on the cytoplasmic fibrils of the NPC initiates hydrolysis of Ran-GTP to Ran-GDP. Ran-GDP induces a conformational change in exportin 1 that weakens its binding to the cargo and the complex disassembles.

After the receptors release the protein in the cytosol, exportin 1 and Ran-GDP move back to the nucleus for subsequent rounds of nuclear export.