title: G-quadruplex formation in telomeres enhances POT1/TPP1 protection against RPA binding.
abstract: Human telomeres terminate with a single-stranded 3' G overhang, which can be recognized as a DNA damage site by replication protein A (RPA). The protection of telomeres (POT1)/POT1-interacting protein 1 (TPP1) heterodimer binds specifically to single-stranded telomeric DNA (ssTEL) and protects G overhangs against RPA binding. The G overhang spontaneously folds into various G-quadruplex (GQ) conformations. It remains unclear whether GQ formation affects the ability of POT1/TPP1 to compete against RPA to access ssTEL. Using single-molecule Förster resonance energy transfer, we showed that POT1 stably loads to a minimal DNA sequence adjacent to a folded GQ. At 150 mM K(+), POT1 loading unfolds the antiparallel GQ, as the parallel conformation remains folded. POT1/TPP1 loading blocks RPA's access to both folded and unfolded telomeres by two orders of magnitude. This protection is not observed at 150 mM Na(+), in which ssTEL forms only a less-stable antiparallel GQ. These results suggest that GQ formation of telomeric overhangs may contribute to suppression of DNA damage signals.
authors: Departments of Physics and Biological Sciences, Kent State University, Kent, OH 44242.
authors: Sujay
authors: S
authors: Ray
authors: Jigar N
authors: JN
authors: Bandaria
authors: Mohammad H
authors: MH
authors: Qureshi
authors: Ahmet
authors: A
authors: Yildiz
authors: Hamza
authors: H
authors: Balci
mesh_terms: D004926:Escherichia coli; D031541:Fluorescence Resonance Energy Transfer; D054856:G-Quadruplexes; D006801:Humans; D008856:Microscopy, Fluorescence; D008958:Models, Molecular; D011487:Protein Conformation; D051716:Replication Protein A / Q000378:metabolism*; D057057:Serine Proteases / Q000737:chemistry / Q000378:metabolism*; D000089804:Shelterin Complex; D016615:Telomere / Q000737:chemistry* / Q000378:metabolism; D034501:Telomere-Binding Proteins / Q000737:chemistry / Q000378:metabolism*
chemical_list: C495876:ACD protein, human; C440849:POT1 protein, human; D051716:Replication Protein A; D000089804:Shelterin Complex; D034501:Telomere-Binding Proteins; D057057:Serine Proteases
keywords: DNA damage response; single molecule imaging; telomere protection