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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 depicting the involvement of two nucleoporin binding regions in importin β in its translocation through the NPC. (A) The two nucleoporin binding regions are illustrated in a ribbon representation of importin β. The NH2-terminal region is shown in blue, and the COOH-terminal region in green. (B) One possible model for importin β translocation through the NPC. The model depicts only the central channel region, but movement between the peripheral fibrils of the NPC and the central channel could be conceptually similar. The two nucleoporin binding regions are shown in blue and green as in A, and the FG-rich nucleoporin regions are depicted as flexible filaments. Importin β could use its NH2- and COOH-terminal regions simultaneously or in succession to promote movement through the NPC.
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fig6: Model depicting the involvement of two nucleoporin binding regions in importin β in its translocation through the NPC. (A) The two nucleoporin binding regions are illustrated in a ribbon representation of importin β. The NH2-terminal region is shown in blue, and the COOH-terminal region in green. (B) One possible model for importin β translocation through the NPC. The model depicts only the central channel region, but movement between the peripheral fibrils of the NPC and the central channel could be conceptually similar. The two nucleoporin binding regions are shown in blue and green as in A, and the FG-rich nucleoporin regions are depicted as flexible filaments. Importin β could use its NH2- and COOH-terminal regions simultaneously or in succession to promote movement through the NPC.

Mentions: Biochemical and functional analysis of a large number of importin β mutants allowed us to characterize the interactions between importin β and several FG repeat nucleoporins. Our data indicate that importin β has a second, previously uncharacterized nucleoporin binding region in its COOH-terminal region (in HEAT repeats 14–16), in addition to the NH2-terminal nucleoporin binding area in HEAT repeats 5–7 that was characterized by crystallographic analysis (Bayliss et al., 2000). Interestingly, the two nucleoporin binding areas are located on the opposite side of the protein (Fig. 6 A), and both regions appear to contribute, to a similar extent, to nuclear import (discussed later).


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

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

Model depicting the involvement of two nucleoporin binding regions in importin β in its translocation through the NPC. (A) The two nucleoporin binding regions are illustrated in a ribbon representation of importin β. The NH2-terminal region is shown in blue, and the COOH-terminal region in green. (B) One possible model for importin β translocation through the NPC. The model depicts only the central channel region, but movement between the peripheral fibrils of the NPC and the central channel could be conceptually similar. The two nucleoporin binding regions are shown in blue and green as in A, and the FG-rich nucleoporin regions are depicted as flexible filaments. Importin β could use its NH2- and COOH-terminal regions simultaneously or in succession to promote movement through the NPC.
© Copyright Policy
Related In: Results  -  Collection

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

fig6: Model depicting the involvement of two nucleoporin binding regions in importin β in its translocation through the NPC. (A) The two nucleoporin binding regions are illustrated in a ribbon representation of importin β. The NH2-terminal region is shown in blue, and the COOH-terminal region in green. (B) One possible model for importin β translocation through the NPC. The model depicts only the central channel region, but movement between the peripheral fibrils of the NPC and the central channel could be conceptually similar. The two nucleoporin binding regions are shown in blue and green as in A, and the FG-rich nucleoporin regions are depicted as flexible filaments. Importin β could use its NH2- and COOH-terminal regions simultaneously or in succession to promote movement through the NPC.
Mentions: Biochemical and functional analysis of a large number of importin β mutants allowed us to characterize the interactions between importin β and several FG repeat nucleoporins. Our data indicate that importin β has a second, previously uncharacterized nucleoporin binding region in its COOH-terminal region (in HEAT repeats 14–16), in addition to the NH2-terminal nucleoporin binding area in HEAT repeats 5–7 that was characterized by crystallographic analysis (Bayliss et al., 2000). Interestingly, the two nucleoporin binding areas are located on the opposite side of the protein (Fig. 6 A), and both regions appear to contribute, to a similar extent, to nuclear import (discussed later).

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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