title: DNA G-quartets in a 1.86 A resolution structure of an Oxytricha nova telomeric protein-DNA complex.
abstract: The Oxytricha nova telomere end binding protein (OnTEBP) recognizes, binds and protects the single-stranded 3'-terminal DNA extension found at the ends of macronuclear chromosomes. The structure of this complex shows that the single strand GGGGTTTTGGGG DNA binds in a deep cleft between the two protein subunits of OnTEBP, adopting a non-helical and irregular conformation. In extending the resolution limit of this structure to 1.86 A, we were surprised to find a G-quartet linked dimer of the GGGGTTTTGGGG DNA also packing within the crystal lattice and interacting with the telomere end binding protein. The G-quartet DNA exhibits the same structure and topology as previously observed in solution by NMR with diagonally crossing d(TTTT) loops at either end of the four-stranded helix. Additionally, the crystal structure reveals clearly visible Na(+), and specific patterns of bound water molecules in the four non-equivalent grooves. Although the G-quartet:protein contact surfaces are modest and might simply represent crystal packing interactions, it is interesting to speculate that the two types of telomeric DNA-protein interactions observed here might both be important in telomere biology.
authors: Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO 80309-0215, USA. Horvath@biology.utah.edu
authors: M P
authors: MP
authors: Horvath
authors: S C
authors: SC
authors: Schultz
mesh_terms: D000818:Animals; D001483:Base Sequence; D002414:Cations, Monovalent / Q000378:metabolism; D018360:Crystallography, X-Ray; D016054:DNA, Protozoan / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000378:metabolism*; D019281:Dimerization; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D010100:Oxygen / Q000378:metabolism; D016813:Oxytricha / Q000737:chemistry / Q000235:genetics; D011485:Protein Binding; D011487:Protein Conformation; D021122:Protein Subunits; D012964:Sodium / Q000378:metabolism; D055672:Static Electricity; D016615:Telomere / Q000235:genetics* / Q000502:physiology; D014867:Water / Q000378:metabolism
chemical_list: D002414:Cations, Monovalent; D016054:DNA, Protozoan; D004268:DNA-Binding Proteins; D021122:Protein Subunits; D014867:Water; D012964:Sodium; D010100:Oxygen