PMID: 22130666

Authors:

Pumroy RA, Nardozzi JD, Hart DJ, Root MJ, Cingolani G

Title:

Nucleoporin Nup50 stabilizes closed conformation of armadillo repeat 10 in importin alpha5.

Journal:

J Biol Chem. 2012 Jan 13;287(3):2022-31. doi: 10.1074/jbc.M111.315838. Epub 2011 , Nov 30.

Abstract:

The human genome encodes six isoforms of importin alpha that show greater than 60% sequence similarity and remarkable substrate specificity. The isoform importin alpha5 can bind phosphorylated cargos such as STAT1 and Epstein-Barr Virus Nuclear Antigen 1, as well as the influenza virus polymerase subunit PB2. In this work, we have studied the interaction of the nucleoporin Nup50 with importin alpha5. We show that the first 47 residues of Nup50 bind to the C terminus of importin alpha5 like a "clip," stabilizing the closed conformation of ARM 10. In vitro, Nup50 binds with high affinity either to empty importin alpha5 or to a preassembled complex of importin alpha5 bound to the C-terminal domain of the import cargo PB2, resulting in a trimeric complex. By contrast, PB2 can only bind with high affinity to importin alpha5 in the absence of Nup50. This suggests that Nup50 primary function may not be to actively displace the import cargo from importin alpha5 but rather to prevent cargo rebinding in preparation for recycling. This is the first evidence for a nucleoporin modulating the import reaction by directly altering the three-dimensional structure of an import adaptor.