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Importin beta contains a COOH-terminal nucleoporin binding region important for nuclear transport.

Bednenko J, Cingolani G, Gerace L - J. Cell Biol. (2003)

Bottom Line: Although the affinity of the COOH-terminal region for nucleoporins is dramatically weaker than that of the NH2-terminal region, sets of mutations that perturb the nucleoporin binding of either region reduce the nuclear import activity of importin beta to a similar extent ( approximately 50%).An importin beta mutant with a combination of mutations in the NH2- and COOH-terminal regions is completely inactive for nuclear import.Thus, importin beta possesses two nucleoporin binding sites, both of which are important for its nuclear import function.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell Biology, The Scripps Research Institute, La Jolla, CA 92037, USA.

ABSTRACT
Proteins containing a classical NLS are transported into the nucleus by the import receptor importin beta, which binds to cargoes via the adaptor importin alpha. The import complex is translocated through the nuclear pore complex by interactions of importin beta with a series of nucleoporins. Previous studies have defined a nucleoporin binding region in the NH2-terminal half of importin beta. Here we report the identification of a second nucleoporin binding region in its COOH-terminal half. Although the affinity of the COOH-terminal region for nucleoporins is dramatically weaker than that of the NH2-terminal region, sets of mutations that perturb the nucleoporin binding of either region reduce the nuclear import activity of importin beta to a similar extent ( approximately 50%). An importin beta mutant with a combination of mutations in the NH2- and COOH-terminal regions is completely inactive for nuclear import. Thus, importin beta possesses two nucleoporin binding sites, both of which are important for its nuclear import function.

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Model of the importin β–IBB domain complex. (A) Rod representation of the structure of importin β complexed with the IBB domain of importin α, according to Cingolani et al. (1999). The A and B helices of the HEAT repeats are shown in red and yellow, respectively, with connecting loops and helices in gray. The IBB domain of importin α is in green. (B) An enlarged view highlighting the A helices of HEAT repeats 5–7, which were shown to be involved in binding FxFG motifs by crystallography (Bayliss et al., 2000). The enlarged image was rotated by 90° in a Y direction with respect to A. The side chains of the residues analyzed by the mutagenesis as described in Table I are highlighted in blue.
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fig1: Model of the importin β–IBB domain complex. (A) Rod representation of the structure of importin β complexed with the IBB domain of importin α, according to Cingolani et al. (1999). The A and B helices of the HEAT repeats are shown in red and yellow, respectively, with connecting loops and helices in gray. The IBB domain of importin α is in green. (B) An enlarged view highlighting the A helices of HEAT repeats 5–7, which were shown to be involved in binding FxFG motifs by crystallography (Bayliss et al., 2000). The enlarged image was rotated by 90° in a Y direction with respect to A. The side chains of the residues analyzed by the mutagenesis as described in Table I are highlighted in blue.

Mentions: Importin β contains 19 tandem HEAT repeats arranged in a superhelical spiral (Cingolani et al., 1999; Fig. 1 A). Each HEAT repeat, which usually has a length of ∼40–60 amino acid residues, consists of A and B helices connected by a short turn. The A helices form the outer surface of importin β, and the B helices create the inner surface. The inner surface of importin β binds to the ∼45-residue importin β binding (IBB) domain of importin α (via HEAT repeats 7–19; Cingolani et al., 1999), the NLS of parathyroid hormone–related protein (PTHrP) (via HEAT repeats 2–11; Cingolani et al., 2002), and RanGTP (via HEAT repeats 1–8; Vetter et al., 1999). The outer surface of importin β contacts FG repeat motifs of nucleoporins (Bayliss et al., 2000, 2002).


Importin beta contains a COOH-terminal nucleoporin binding region important for nuclear transport.

Bednenko J, Cingolani G, Gerace L - J. Cell Biol. (2003)

Model of the importin β–IBB domain complex. (A) Rod representation of the structure of importin β complexed with the IBB domain of importin α, according to Cingolani et al. (1999). The A and B helices of the HEAT repeats are shown in red and yellow, respectively, with connecting loops and helices in gray. The IBB domain of importin α is in green. (B) An enlarged view highlighting the A helices of HEAT repeats 5–7, which were shown to be involved in binding FxFG motifs by crystallography (Bayliss et al., 2000). The enlarged image was rotated by 90° in a Y direction with respect to A. The side chains of the residues analyzed by the mutagenesis as described in Table I are highlighted in blue.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2172684&req=5

fig1: Model of the importin β–IBB domain complex. (A) Rod representation of the structure of importin β complexed with the IBB domain of importin α, according to Cingolani et al. (1999). The A and B helices of the HEAT repeats are shown in red and yellow, respectively, with connecting loops and helices in gray. The IBB domain of importin α is in green. (B) An enlarged view highlighting the A helices of HEAT repeats 5–7, which were shown to be involved in binding FxFG motifs by crystallography (Bayliss et al., 2000). The enlarged image was rotated by 90° in a Y direction with respect to A. The side chains of the residues analyzed by the mutagenesis as described in Table I are highlighted in blue.
Mentions: Importin β contains 19 tandem HEAT repeats arranged in a superhelical spiral (Cingolani et al., 1999; Fig. 1 A). Each HEAT repeat, which usually has a length of ∼40–60 amino acid residues, consists of A and B helices connected by a short turn. The A helices form the outer surface of importin β, and the B helices create the inner surface. The inner surface of importin β binds to the ∼45-residue importin β binding (IBB) domain of importin α (via HEAT repeats 7–19; Cingolani et al., 1999), the NLS of parathyroid hormone–related protein (PTHrP) (via HEAT repeats 2–11; Cingolani et al., 2002), and RanGTP (via HEAT repeats 1–8; Vetter et al., 1999). The outer surface of importin β contacts FG repeat motifs of nucleoporins (Bayliss et al., 2000, 2002).

Bottom Line: Although the affinity of the COOH-terminal region for nucleoporins is dramatically weaker than that of the NH2-terminal region, sets of mutations that perturb the nucleoporin binding of either region reduce the nuclear import activity of importin beta to a similar extent ( approximately 50%).An importin beta mutant with a combination of mutations in the NH2- and COOH-terminal regions is completely inactive for nuclear import.Thus, importin beta possesses two nucleoporin binding sites, both of which are important for its nuclear import function.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell Biology, The Scripps Research Institute, La Jolla, CA 92037, USA.

ABSTRACT
Proteins containing a classical NLS are transported into the nucleus by the import receptor importin beta, which binds to cargoes via the adaptor importin alpha. The import complex is translocated through the nuclear pore complex by interactions of importin beta with a series of nucleoporins. Previous studies have defined a nucleoporin binding region in the NH2-terminal half of importin beta. Here we report the identification of a second nucleoporin binding region in its COOH-terminal half. Although the affinity of the COOH-terminal region for nucleoporins is dramatically weaker than that of the NH2-terminal region, sets of mutations that perturb the nucleoporin binding of either region reduce the nuclear import activity of importin beta to a similar extent ( approximately 50%). An importin beta mutant with a combination of mutations in the NH2- and COOH-terminal regions is completely inactive for nuclear import. Thus, importin beta possesses two nucleoporin binding sites, both of which are important for its nuclear import function.

Show MeSH
Related in: MedlinePlus