Ran

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Ran is a GTP-binding protein which forms complexes with karyopherins which play a role in cargo exchange between the nucleus and cytoplasm of eukaryotes[1].

Ran proteins undergo a conformational change when bound to either GTP or GDP so it is able to participate in both protein import and export. Ran-GTP molecules exclusively bind to karyopherins referred to as exportins to move target proteins into the cytoplasm[1]. A GTPase activating protein catalyzes the hydrolysis of the bound GTP to GDP[2]. Exportins have a much lower affinity for Ran-GDP resulting in the release of the Ran molecule. This reverses the conformational change of exportin, releasing the cargo. Exportin complexes normally carry immature RNA strands to the cytoplasm to be modified and spliced prior to translation[3].

Ran-GDP binds to importins and as its name suggests, imports target proteins such as histones into the nuclease. Guanine exchange factors such as RCC1 catalyses the conversion of GDP to GTP which reduces the affinity of the transporting for the Ran protein, thus releasing target proteins such as histones and steroid hormones into the nucleus[4][1].

References

  1. 1.0 1.1 1.2 Macara I. Transport into and out of the Nucleus. Microbiology and Molecular Biology Reviews [Internet]. 2001 [cited 3 December 2017];65(4):570-594. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC99041/
  2. Rudack T, Xia F, Schlitter J, Kotting C, Gerwert K. Ras and GTPase-activating protein (GAP) drive GTP into a precatalytic state as revealed by combining FTIR and biomolecular simulations. Proceedings of the National Academy of Sciences [Internet]. 2012 [cited 3 December 2017];109(38):15295-15300. Available from: https://www.ncbi.nlm.nih.gov/pubmed/22949691
  3. Ren M, Villamarin A, Shih A, Coutavas E, Moore M, LoCurcio M et al. Separate domains of the Ran GTPase interact with different factors to regulate nuclear protein import and RNA processing. Molecular and Cellular Biology [Internet]. 1995;15(4):2117-2124. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC230439/pdf/152117.pdf
  4. Moore M. Ran and Nuclear Transport [Internet]. Journal of Biological Science. 2017 [cited 3 December 2017]. Available from: http://www.jbc.org/content/273/36/22857.full.html
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