PDBsum entry 3knd

Protein transport

PDB id: 3knd

Contents

Protein chains

428 a.a. *

16 a.a. *

Ligands

SO4 ×5

Waters ×236

* Residue conservation analysis

PDB id:

3knd

Name:

Protein transport

Title:

Tpx2:importin-alpha complex

Structure:

Importin subunit alpha-2. Chain: a. Fragment: residues 70-529. Synonym: karyopherin subunit alpha-2, srp1-alpha, rag cohort protein 1, pendulin, pore targeting complex 58 kda subunit, ptac58, importin alpha p1. Engineered: yes. Targeting protein for xklp2. Chain: b.

Source:

Mus musculus. Mouse. Organism_taxid: 10090. Gene: importin alpha 2, kpna2, rch1. Expressed in: escherichia coli. Expression_system_taxid: 562. Xenopus laevis. Platanna. Organism_taxid: 8355.

Resolution:

2.15Å R-factor: 0.185 R-free: 0.214

Authors:

M.Stewart

Key ref:

A.Giesecke and M.Stewart (2010). Novel binding of the mitotic regulator TPX2 (target protein for Xenopus kinesin-like protein 2) to importin-alpha. J Biol Chem, 285, 17628-17635. PubMed id: 20335181

Date:

12-Nov-09 Release date: 23-Mar-10

Protein chain

P52293  (IMA1_MOUSE) -  Importin subunit alpha-1 from Mus musculus

Seq: 529 a.a.

Struc: 428 a.a.

Protein chain

Q6NUF4  (TPX2A_XENLA) -  Targeting protein for Xklp2-A from Xenopus laevis

Seq: 716 a.a.

Struc: 16 a.a.*

* PDB and UniProt seqs differ at 4 residue positions (black crosses)

J Biol Chem 285:17628-17635 (2010)

PubMed id: 20335181

Novel binding of the mitotic regulator TPX2 (target protein for Xenopus kinesin-like protein 2) to importin-alpha.

A.Giesecke, M.Stewart.

ABSTRACT

Several aspects of mitotic spindle assembly are orchestrated by the Ran GTPase through its modulation of the interaction between spindle assembly factors and importin-alpha. One such factor is TPX2 that promotes microtubule assembly in the vicinity of chromosomes. TPX2 is inhibited when bound to importin-alpha, which occurs when the latter is bound to importin-beta. The importin-alpha:beta interaction is disrupted by the high RanGTP concentration near the chromosomes, releasing TPX2. In more distal regions, where Ran is predominantly GDP-bound, TPX2 remains bound to importin-alpha and so is inhibited. Here we use a combination of structural and biochemical methods to define the basis for TPX2 binding to importin-alpha. A 2.2 A resolution crystal structure shows that the primary nuclear localization signal ((284)KRKH(287)) of TPX2, which has been shown to be crucial for inhibition, binds to the minor NLS-binding site on importin-alpha. This atypical interaction pattern was confirmed using complementary binding studies that employed importin-alpha variants in which binding to either the major or minor NLS-binding site was impaired, together with competition assays using the SV40 monopartite NLS that binds primarily to the major site. The different way in which TPX2 binds to importin-alpha could account for much of the selectivity necessary during mitosis because this would reduce the competition for binding to importin-alpha from other NLS-containing proteins.