5owu | pdb_00005owu
Kap95:Nup1 complex
Structural highlights
Function[IMB1_YEAST] Required for nuclear protein import and mediates docking of import substrate to distinct nucleoporins. Serves a receptor for nuclear localization signals. Mediates the nuclear import of histones H2A and H2B.[1] [NUP1_YEAST] Functions as a component of the nuclear pore complex (NPC). NPC components, collectively referred to as nucleoporins (NUPs), can play the role of both NPC structural components and of docking or interaction partners for transiently associated nuclear transport factors. Active directional transport is assured by both, a Phe-Gly (FG) repeat affinity gradient for these transport factors across the NPC and a transport cofactor concentration gradient across the nuclear envelope (GSP1 and GSP2 GTPases associated predominantly with GTP in the nucleus, with GDP in the cytoplasm). As one of the FG repeat nucleoporins NUP1 is involved in interactions with and guidance of nuclear transport receptors such as SRP1-KAP95 (importin alpha and beta) through the NPC. Like the closely related NUP2 it also plays an important role in disassembling and recycling SRP1-KAP95 to the cytoplasm after nuclear import. Upon entry of the heterotrimeric SRP1-KAP95-cargo complex in the nucleus, NUP1 binds through its C-terminus to KAP95, thus accelerating the release of KAP95 and, indirectly, of the nuclear localization signal (NLS)-containing cargo from the SRP1-KAP95-cargo complex.[2] [3] [4] [5] [6] [7] [8] [9] [10] Publication Abstract from PubMedMacromolecules are transported across the nuclear envelope most frequently by karyopherin/importin-beta superfamily members that are constructed from HEAT repeats. Transport of Kap95p (yeast importin-beta), the principal carrier for protein import, through nuclear pore complexes is facilitated by interactions with nucleoporins containing FG repeats. However, Nup1p interacts more strongly with Kap95p than other FG-nucleoporins. To establish the basis of this increased affinity, we determined the structure of Kap95p complexed with Nup1p residues 963-1076 that contain the high-affinity Kap95p binding site. Nup1p binds Kap95p at three sites between the outer A-helices of HEAT repeats 5, 6, 7 and 8. At each site, phenylalanine residues from Nup1p are buried in hydrophobic depressions between adjacent HEAT repeats. Although the Nup1p and generic FG-nucleoporin binding sites on Kap95p overlap, Nup1p binding differs markedly and has contributions from additional hydrophobic residues, together with interactions generated by the intimate contact of the linker between Nup1 residues 977-987 with Kap95p. The length and composition of this linker is crucial and suggests how differences in affinity for Kap95p both between and within FG-nucleoporins arise. Structural basis for the high-affinity binding of nucleoporin Nup1p to the Saccharomyces cerevisiae importin-beta homologue, Kap95p.,Liu SM, Stewart M J Mol Biol. 2005 Jun 10;349(3):515-25. Epub 2005 Apr 19. PMID:15878174[11] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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