5kea | pdb_00005kea
mouse Klf4 ZnF1-3 (E446D) and CpG/CpG sequence DNA complex structure: Form I
Structural highlights
Function[KLF4_MOUSE] Transcription factor; can act both as activator and as repressor. Binds the 5'-CACCC-3' core sequence. Binds to the promoter region of its own gene and can activate its own transcription. Regulates the expression of key transcription factors during embryonic development. Plays an important role in maintaining embryonic stem cells, and in preventing their differentiation. Required for establishing the barrier function of the skin and for postnatal maturation and maintenance of the ocular surface. Involved in the differentiation of epithelial cells and may also function in skeletal and kidney development. Contributes to the down-regulation of p53/TP53 transcription (By similarity).[1] [2] [3] [4] [5] [6] [7] Publication Abstract from PubMedReprogramming of mammalian genome methylation is critically important but poorly understood. Klf4, a transcription factor directing reprogramming, contains a DNA binding domain with three consecutive C2H2 zinc fingers. Klf4 recognizes CpG or TpG within a specific sequence. Mouse Klf4 DNA binding domain has roughly equal affinity for methylated CpG or TpG, and slightly lower affinity for unmodified CpG. The structural basis for this key preference is unclear, though the side chain of Glu446 is known to contact the methyl group of 5-methylcytosine (5mC) or thymine (5-methyluracil). We examined the role of Glu446 by mutagenesis. Substituting Glu446 with aspartate (E446D) resulted in preference for unmodified cytosine, due to decreased affinity for 5mC. In contrast, substituting Glu446 with proline (E446P) increased affinity for 5mC by two orders of magnitude. Structural analysis revealed hydrophobic interaction between the proline's aliphatic cyclic structure and the 5-methyl group of the pyrimidine (5mC or T). As in wild-type Klf4 (E446), the proline at position 446 does not interact directly with either the 5mC N4 nitrogen or the thymine O4 oxygen. In contrast, the unmethylated cytosine's exocyclic N4 amino group (NH2) and its ring carbon C5 atom hydrogen bond directly with the aspartate carboxylate of the E446D variant. Both of these interactions would provide a preference for cytosine over thymine, and the latter one could explain the E446D preference for unmethylated cytosine. Finally, we evaluated the ability of these Klf4 mutants to regulate transcription of methylated and unmethylated promoters in a luciferase reporter assay. Distinctive Klf4 mutants determine preference for DNA methylation status.,Hashimoto H, Wang D, Steves AN, Jin P, Blumenthal RM, Zhang X, Cheng X Nucleic Acids Res. 2016 Sep 4. pii: gkw774. PMID:27596594[8] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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