title: SKN-1 domain folding and basic region monomer stabilization upon DNA binding.
abstract: The SKN-1 transcription factor specifies early embryonic cell fates in Caenorhabditis elegans. SKN-1 binds DNA at high affinity as a monomer, by means of a basic region like those of basic-leucine zipper (bZIP) proteins, which bind DNA only as dimers. We have investigated how the SKN-1 DNA-binding domain (the Skn domain) promotes stable binding of a basic region monomer to DNA. A flexible arm at the Skn domain amino terminus binds in the minor groove, but a support segment adjacent to the carboxy-terminal basic region can independently stabilize basic region-DNA binding. Off DNA, the basic region and arm are unfolded and, surprisingly, the support segment forms a molten globule of four alpha-helices. On binding DNA, the Skn domain adopts a tertiary structure in which the basic region helix extends directly from a support segment alpha-helix, which is required for binding. The remainder of the support segment anchors this uninterrupted helix on DNA, but leaves the basic region exposed in the major groove. This is similar to how the bZIP basic region extends from the leucine zipper, indicating that positioning and cooperative stability provided by helix extension are conserved mechanisms that promote binding of basic regions to DNA.
authors.affiliation: Center for Blood Research and Department of Pathology, Harvard Medical School, Boston, Massachusetts 02115, USA.
authors.forename: A S
authors.initials: AS
authors.lastname: Carroll
authors.forename: D E
authors.initials: DE
authors.lastname: Gilbert
authors.forename: X
authors.initials: X
authors.lastname: Liu
authors.forename: J W
authors.initials: JW
authors.lastname: Cheung
authors.forename: J E
authors.initials: JE
authors.lastname: Michnowicz
authors.forename: G
authors.initials: G
authors.lastname: Wagner
authors.forename: T E
authors.initials: TE
authors.lastname: Ellenberger
authors.forename: T K
authors.initials: TK
authors.lastname: Blackwell
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D017173:Caenorhabditis elegans / Q000196:embryology / Q000235:genetics / Q000378:metabolism; D029742:Caenorhabditis elegans Proteins; D004247:DNA / Q000737:chemistry / Q000378:metabolism*; D004268:DNA-Binding Proteins; D015801:Helminth Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009690:Nucleic Acid Conformation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D014157:Transcription Factors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: D029742:Caenorhabditis elegans Proteins; D004268:DNA-Binding Proteins; D015801:Helminth Proteins; D014157:Transcription Factors; C073702:skn-1 protein, C elegans; D004247:DNA