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Crystal structure of the human FOXO3a-DBD/DNA complex suggests the effects of post-translational modification.

Tsai KL, Sun YJ, Huang CY, Yang JY, Hung MC, Hsiao CD - Nucleic Acids Res. (2007)

Bottom Line: Because these post-translational modification sites are located within the C-terminal basic region of the FOXO DNA-binding domain (FOXO-DBD), it is possible that these post-translational modifications could alter the DNA-binding characteristics.Based on a unique structural feature in the C-terminal region and results from biochemical and mutational studies, our studies may explain how FOXO-DBD C-terminal phosphorylation by protein kinase B (PKB) or acetylation by cAMP-response element binding protein (CBP) can attenuate the DNA-binding activity and thereby reduce transcriptional activity of FOXO proteins.In addition, we demonstrate that the methyl groups of specific thymine bases within the consensus sequence are important for FOXO3a-DBD recognition of the consensus binding site.

View Article: PubMed Central - PubMed

Affiliation: Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan.

ABSTRACT
FOXO3a is a transcription factor of the FOXO family. The FOXO proteins participate in multiple signaling pathways, and their transcriptional activity is regulated by several post-translational mechanisms, including phosphorylation, acetylation and ubiquitination. Because these post-translational modification sites are located within the C-terminal basic region of the FOXO DNA-binding domain (FOXO-DBD), it is possible that these post-translational modifications could alter the DNA-binding characteristics. To understand how FOXO mediate transcriptional activity, we report here the 2.7 A crystal structure of the DNA-binding domain of FOXO3a (FOXO3a-DBD) bound to a 13-bp DNA duplex containing a FOXO consensus binding sequence (GTAAACA). Based on a unique structural feature in the C-terminal region and results from biochemical and mutational studies, our studies may explain how FOXO-DBD C-terminal phosphorylation by protein kinase B (PKB) or acetylation by cAMP-response element binding protein (CBP) can attenuate the DNA-binding activity and thereby reduce transcriptional activity of FOXO proteins. In addition, we demonstrate that the methyl groups of specific thymine bases within the consensus sequence are important for FOXO3a-DBD recognition of the consensus binding site.

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Schematic representation of FOXO3a and sequence alignment of its forkhead domain with other FOX proteins. (A) Schematic domain structure of FOXO3a. Forkhead domain and NLS are colored yellow and red, respectively. (B) Sequence alignment of the forkhead DNA-binding domains from FOXO3a, FOXO1, FOXA3, FOXK1a and FOXP2 are shown with reference to the residue numbers and secondary structural elements of FOXO3a (black cylinders, α-helices; yellow arrows, β-strands). The amino acids of helix 3 that are highly conserved in the winged helix/forkhead family are boxed in red. Residues that are identical or similar among family members are shaded in blue and yellow, respectively.
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Figure 1: Schematic representation of FOXO3a and sequence alignment of its forkhead domain with other FOX proteins. (A) Schematic domain structure of FOXO3a. Forkhead domain and NLS are colored yellow and red, respectively. (B) Sequence alignment of the forkhead DNA-binding domains from FOXO3a, FOXO1, FOXA3, FOXK1a and FOXP2 are shown with reference to the residue numbers and secondary structural elements of FOXO3a (black cylinders, α-helices; yellow arrows, β-strands). The amino acids of helix 3 that are highly conserved in the winged helix/forkhead family are boxed in red. Residues that are identical or similar among family members are shaded in blue and yellow, respectively.

Mentions: The forkhead box proteins (FOX proteins) comprise a large family of functionally diverse transcription factors involved in cellular proliferation, transformation, differentiation and longevity (1–3). These proteins, found in various species ranging from yeast to human, have multiple domains that are specific for DNA binding, transactivation or transrepression (4). One sub-family of FOX proteins, the ‘O’ class forkhead proteins (FOXO), are transcription factors that play important roles in several biological processes, including metabolism, cellular proliferation, cell survival and response to oxidative stress (5–10). To date, the FOXO family in mammals contains four members: FOXO1 (FKHR), FOXO3a (FKHRL1), FOXO4 (AFX) and FOXO6. These proteins share a high degree of evolutionary conservation, especially in the forkhead DNA-binding domain (Figure 1A and B) (11–14). Among these FOXO proteins, FOXO3a is involved in cell transformation, tumor progression and angiogenesis (15–17).Figure 1.


Crystal structure of the human FOXO3a-DBD/DNA complex suggests the effects of post-translational modification.

Tsai KL, Sun YJ, Huang CY, Yang JY, Hung MC, Hsiao CD - Nucleic Acids Res. (2007)

Schematic representation of FOXO3a and sequence alignment of its forkhead domain with other FOX proteins. (A) Schematic domain structure of FOXO3a. Forkhead domain and NLS are colored yellow and red, respectively. (B) Sequence alignment of the forkhead DNA-binding domains from FOXO3a, FOXO1, FOXA3, FOXK1a and FOXP2 are shown with reference to the residue numbers and secondary structural elements of FOXO3a (black cylinders, α-helices; yellow arrows, β-strands). The amino acids of helix 3 that are highly conserved in the winged helix/forkhead family are boxed in red. Residues that are identical or similar among family members are shaded in blue and yellow, respectively.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

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Figure 1: Schematic representation of FOXO3a and sequence alignment of its forkhead domain with other FOX proteins. (A) Schematic domain structure of FOXO3a. Forkhead domain and NLS are colored yellow and red, respectively. (B) Sequence alignment of the forkhead DNA-binding domains from FOXO3a, FOXO1, FOXA3, FOXK1a and FOXP2 are shown with reference to the residue numbers and secondary structural elements of FOXO3a (black cylinders, α-helices; yellow arrows, β-strands). The amino acids of helix 3 that are highly conserved in the winged helix/forkhead family are boxed in red. Residues that are identical or similar among family members are shaded in blue and yellow, respectively.
Mentions: The forkhead box proteins (FOX proteins) comprise a large family of functionally diverse transcription factors involved in cellular proliferation, transformation, differentiation and longevity (1–3). These proteins, found in various species ranging from yeast to human, have multiple domains that are specific for DNA binding, transactivation or transrepression (4). One sub-family of FOX proteins, the ‘O’ class forkhead proteins (FOXO), are transcription factors that play important roles in several biological processes, including metabolism, cellular proliferation, cell survival and response to oxidative stress (5–10). To date, the FOXO family in mammals contains four members: FOXO1 (FKHR), FOXO3a (FKHRL1), FOXO4 (AFX) and FOXO6. These proteins share a high degree of evolutionary conservation, especially in the forkhead DNA-binding domain (Figure 1A and B) (11–14). Among these FOXO proteins, FOXO3a is involved in cell transformation, tumor progression and angiogenesis (15–17).Figure 1.

Bottom Line: Because these post-translational modification sites are located within the C-terminal basic region of the FOXO DNA-binding domain (FOXO-DBD), it is possible that these post-translational modifications could alter the DNA-binding characteristics.Based on a unique structural feature in the C-terminal region and results from biochemical and mutational studies, our studies may explain how FOXO-DBD C-terminal phosphorylation by protein kinase B (PKB) or acetylation by cAMP-response element binding protein (CBP) can attenuate the DNA-binding activity and thereby reduce transcriptional activity of FOXO proteins.In addition, we demonstrate that the methyl groups of specific thymine bases within the consensus sequence are important for FOXO3a-DBD recognition of the consensus binding site.

View Article: PubMed Central - PubMed

Affiliation: Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan.

ABSTRACT
FOXO3a is a transcription factor of the FOXO family. The FOXO proteins participate in multiple signaling pathways, and their transcriptional activity is regulated by several post-translational mechanisms, including phosphorylation, acetylation and ubiquitination. Because these post-translational modification sites are located within the C-terminal basic region of the FOXO DNA-binding domain (FOXO-DBD), it is possible that these post-translational modifications could alter the DNA-binding characteristics. To understand how FOXO mediate transcriptional activity, we report here the 2.7 A crystal structure of the DNA-binding domain of FOXO3a (FOXO3a-DBD) bound to a 13-bp DNA duplex containing a FOXO consensus binding sequence (GTAAACA). Based on a unique structural feature in the C-terminal region and results from biochemical and mutational studies, our studies may explain how FOXO-DBD C-terminal phosphorylation by protein kinase B (PKB) or acetylation by cAMP-response element binding protein (CBP) can attenuate the DNA-binding activity and thereby reduce transcriptional activity of FOXO proteins. In addition, we demonstrate that the methyl groups of specific thymine bases within the consensus sequence are important for FOXO3a-DBD recognition of the consensus binding site.

Show MeSH