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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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Structural alignment of the NH2- and COOH-terminal segments of importin β. (A) Worm representation of importin β. Residues 1–445 are highlighted in gray and residues 446–876 are in green. (B) Alignment of the NH2- and COOH-terminal segments of importin β. Residues 1–445 (HEAT repeats 1–10) are in gray and residues 446–876 (HEAT repeats 11–19) are in green. (C) The side chains of importin β residues I178, Y255, and I263 (yellow) closely align with those of L612, F688, and L695 (red), respectively. The enlarged image in C was rotated 90° in a Y direction and 30° in a Z direction with respect to B.
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fig4: Structural alignment of the NH2- and COOH-terminal segments of importin β. (A) Worm representation of importin β. Residues 1–445 are highlighted in gray and residues 446–876 are in green. (B) Alignment of the NH2- and COOH-terminal segments of importin β. Residues 1–445 (HEAT repeats 1–10) are in gray and residues 446–876 (HEAT repeats 11–19) are in green. (C) The side chains of importin β residues I178, Y255, and I263 (yellow) closely align with those of L612, F688, and L695 (red), respectively. The enlarged image in C was rotated 90° in a Y direction and 30° in a Z direction with respect to B.

Mentions: To further analyze the nucleoporin binding site contained within the COOH-terminal fragment of importin β, we attempted to identify the COOH-terminal amino acid residues involved in nucleoporin binding. Initially, we performed an intramolecular structural alignment of the NH2-terminal (HEAT repeats 1–10) and the COOH-terminal (HEAT repeats 11–19) fragments of importin β (Fig. 4, A and B). The two polypeptide chains were aligned using the combinatorial extension (CE) method, which determines an optimal alignment between fragment pairs (Shindyalov and Bourne, 1998). Interestingly, we found that the importin β regions containing residues 1–445 and 446–876 were structurally similar and could be superimposed with a root mean square deviation for the α carbon chains of ∼3.4 Å (Fig. 4 B). The central HEAT repeats (4–7 and 13–16) presented the highest structural homology (root mean square deviation for the α carbon chains of ∼2.1 Å), whereas the HEAT repeats located to the periphery of these core regions showed the highest divergence (Fig. 4 B).


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

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

Structural alignment of the NH2- and COOH-terminal segments of importin β. (A) Worm representation of importin β. Residues 1–445 are highlighted in gray and residues 446–876 are in green. (B) Alignment of the NH2- and COOH-terminal segments of importin β. Residues 1–445 (HEAT repeats 1–10) are in gray and residues 446–876 (HEAT repeats 11–19) are in green. (C) The side chains of importin β residues I178, Y255, and I263 (yellow) closely align with those of L612, F688, and L695 (red), respectively. The enlarged image in C was rotated 90° in a Y direction and 30° in a Z direction with respect to B.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2172684&req=5

fig4: Structural alignment of the NH2- and COOH-terminal segments of importin β. (A) Worm representation of importin β. Residues 1–445 are highlighted in gray and residues 446–876 are in green. (B) Alignment of the NH2- and COOH-terminal segments of importin β. Residues 1–445 (HEAT repeats 1–10) are in gray and residues 446–876 (HEAT repeats 11–19) are in green. (C) The side chains of importin β residues I178, Y255, and I263 (yellow) closely align with those of L612, F688, and L695 (red), respectively. The enlarged image in C was rotated 90° in a Y direction and 30° in a Z direction with respect to B.
Mentions: To further analyze the nucleoporin binding site contained within the COOH-terminal fragment of importin β, we attempted to identify the COOH-terminal amino acid residues involved in nucleoporin binding. Initially, we performed an intramolecular structural alignment of the NH2-terminal (HEAT repeats 1–10) and the COOH-terminal (HEAT repeats 11–19) fragments of importin β (Fig. 4, A and B). The two polypeptide chains were aligned using the combinatorial extension (CE) method, which determines an optimal alignment between fragment pairs (Shindyalov and Bourne, 1998). Interestingly, we found that the importin β regions containing residues 1–445 and 446–876 were structurally similar and could be superimposed with a root mean square deviation for the α carbon chains of ∼3.4 Å (Fig. 4 B). The central HEAT repeats (4–7 and 13–16) presented the highest structural homology (root mean square deviation for the α carbon chains of ∼2.1 Å), whereas the HEAT repeats located to the periphery of these core regions showed the highest divergence (Fig. 4 B).

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