Structures of Importins and Exportins

Abstract

The karyopherin-β (Kap) family of nuclear transport receptors mediates the majority of nuclear-cytoplasmic transport of macromolecules, especially that of proteins. Kaps include importins that transport cargos into the nucleus, exportins that transport cargos out of the nucleus, and bidirectional Kaps that transport one set of cargos into the nucleus and another set of cargos out of the nucleus. The binding of transport cargos to Kaps and the release of cargos from Kaps are controlled by the Ran GTPase, hence dependent on the RanGTP–RanGDP gradient in cells. Many structures of the import adaptor importin-α complexes and of ten different Kaps are available. This chapter begins covers nucleotide-specific conformational differences of the Ran GTPase, structural information on importin-α and of ten different Kaps describing how each protein recognizes cargo(s), how Ran affects Kap-cargo interactions, and in a few cases how Kaps interact with nucleoporins.