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#Ran GTPase

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Protein Sorting and Trafficking

The major energy source for nuclear transport is:

Energy input driving selective accumulation of proteins inside nucleus does not come from kinesin ATP hydrolysis used for microtubule transport or proton motive force powering mitochondrial import, but from compartmentalized GTP turnover of Ran. RCC1 guanine exchange factor bound to nucleosomes continuously recharges Ran-GDP to Ran-GTP using nuclear GTP pool, while cytoplasmic RanGAP1 SUMOylated and anchored to RanBP2/Nup358 plus co-activator RanBP1 hydrolyze GTP outside. Each import cycle consumes one GTP upon export complex disassembly in cytosol, and each export cycle consumes GTP as Ran-GT

Ref: NCBI Bookshelf, Molecular Biology of the Cell, Section: GTP Hydrolysis by Ran as Energy Source.

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Protein Sorting and Trafficking

The export of proteins from the nucleus requires:

Export of proteins from the nucleus depends on recognition of leucine-rich nuclear export signals that provide dominant cue for exit to the cytoplasm. Canonical NES consists of short amphipathic alpha-helix with regularly spaced large hydrophobic residues, typically leucine, isoleucine, valine or phenylalanine, arranged in pattern Φ-X2-3-Φ-X2-3-Φ-X-Φ where Φ denotes hydrophobic. This motif docks into hydrophobic groove formed by HEAT repeats 11 and 12 of chromosome region maintenance 1, CRM1, also called Exportin-1 or XPO1, stabilized only when Ran is in GTP-bound state present at high concent

Ref: Lodish et al., Molecular Cell Biology, 9th ed., Chapter 13: CRM1 Exportin Recognition of Leucine-Rich NES.

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