title: Electron microscopy studies on the quaternary structure of p53 reveal different binding modes for p53 tetramers in complex with DNA.
abstract: The multidomain homotetrameric tumor suppressor p53 has two modes of binding dsDNA that are thought to be responsible for scanning and recognizing specific response elements (REs). The C termini bind nonspecifically to dsDNA. The four DNA-binding domains (DBDs) bind REs that have two symmetric 10 base-pair sequences. p53 bound to a 20-bp RE has the DBDs enveloping the DNA, which is in the center of the molecule surrounded by linker sequences to the tetramerization domain (Tet). We investigated by electron microscopy structures of p53 bound to DNA sequences consisting of a 20-bp RE with either 12 or 20 bp nonspecific extensions on either end. We found a variety of structures that give clues to recognition and scanning mechanisms. The 44- and 60-bp sequences gave rise to three and four classes of structures, respectively. One was similar to the known 20-bp structure, but the DBDs in the other classes were loosely arranged and incompatible with specific DNA recognition. Some of the complexes had density consistent with the C termini extending from Tet to the DNA, adjacent to the DBDs. Single-molecule fluorescence resonance energy transfer experiments detected the approach of the C termini towards the DBDs on addition of DNA. The structural data are consistent with p53 sliding along DNA via its C termini and the DNA-binding domains hopping on and off during searches for REs. The loose structures and posttranslational modifications account for the affinity of nonspecific DNA for p53 and point to a mechanism of enhancement of specificity by its binding to effector proteins.
authors.affiliation: Centro Nacional de Biotecnología, Darwin 3, 28049 Madrid, Spain.
authors.forename: Roberto
authors.initials: R
authors.lastname: Melero
authors.forename: Sridharan
authors.initials: S
authors.lastname: Rajagopalan
authors.forename: Melisa
authors.initials: M
authors.lastname: Lázaro
authors.forename: Andreas C
authors.initials: AC
authors.lastname: Joerger
authors.forename: Tobias
authors.initials: T
authors.lastname: Brandt
authors.forename: Dmitry B
authors.initials: DB
authors.lastname: Veprintsev
authors.forename: Gorka
authors.initials: G
authors.lastname: Lasso
authors.forename: David
authors.initials: D
authors.lastname: Gil
authors.forename: Sjors H W
authors.initials: SH
authors.lastname: Scheres
authors.forename: José María
authors.initials: JM
authors.lastname: Carazo
authors.forename: Alan R
authors.initials: AR
authors.lastname: Fersht
authors.forename: Mikel
authors.initials: M
authors.lastname: Valle
mesh_terms: D000409:Alanine / Q000737:chemistry; D003553:Cystine / Q000737:chemistry; D004247:DNA / Q000737:chemistry*; D031541:Fluorescence Resonance Energy Transfer; D016158:Genes, p53; D006801:Humans; D008854:Microscopy, Electron / Q000379:methods*; D009154:Mutation; D009690:Nucleic Acid Conformation; D011485:Protein Binding; D011487:Protein Conformation; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D016159:Tumor Suppressor Protein p53 / Q000737:chemistry*
chemical_list: C495901:TP53 protein, human; D016159:Tumor Suppressor Protein p53; D003553:Cystine; D004247:DNA; D000409:Alanine