title: Telomere Recognition and Assembly Mechanism of Mammalian Shelterin.
abstract: Shelterin is a six-subunit protein complex that plays crucial roles in telomere length regulation, protection, and maintenance. Although several shelterin subunits have been studied in vitro, the biochemical properties of the fully assembled shelterin complex are not well defined. Here, we characterize shelterin using ensemble biochemical methods, electron microscopy, and single-molecule imaging to determine how shelterin recognizes and assembles onto telomeric repeats. We show that shelterin complexes can exist in solution and primarily locate telomeric DNA through a three-dimensional diffusive search. Shelterin can diffuse along non-telomeric DNA but is impeded by nucleosomes, arguing against extensive one-dimensional diffusion as a viable assembly mechanism. Our work supports a model in which individual shelterin complexes rapidly bind to telomeric repeats as independent functional units, which do not alter the DNA-binding mode of neighboring complexes but, rather, occupy telomeric DNA in a "beads on a string" configuration.
authors.affiliation: Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA.
authors.forename: Fabian
authors.initials: F
authors.lastname: Erdel
authors.affiliation: Laboratory for Cell Biology and Genetics, Rockefeller University, New York, NY 10065, USA.
authors.forename: Katja
authors.initials: K
authors.lastname: Kratz
authors.affiliation: Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
authors.forename: Smaranda
authors.initials: S
authors.lastname: Willcox
authors.affiliation: Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
authors.forename: Jack D
authors.initials: JD
authors.lastname: Griffith
authors.affiliation: Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA. Electronic address: ecg2108@cumc.columbia.edu.
authors.forename: Eric C
authors.initials: EC
authors.lastname: Greene
authors.affiliation: Laboratory for Cell Biology and Genetics, Rockefeller University, New York, NY 10065, USA. Electronic address: delange@rockefeller.edu.
authors.forename: Titia
authors.initials: T
authors.lastname: de Lange
mesh_terms: D000818:Animals; D004247:DNA / Q000378:metabolism; D004058:Diffusion; D057809:HEK293 Cells; D006801:Humans; D007700:Kinetics; D008322:Mammals / Q000378:metabolism*; D046912:Multiprotein Complexes / Q000378:metabolism; D011485:Protein Binding; D012091:Repetitive Sequences, Nucleic Acid; D016615:Telomere / Q000378:metabolism*; D034501:Telomere-Binding Proteins / Q000378:metabolism*; D035341:Telomeric Repeat Binding Protein 2 / Q000378:metabolism; D020827:rap1 GTP-Binding Proteins / Q000378:metabolism
chemical_list: D046912:Multiprotein Complexes; D034501:Telomere-Binding Proteins; D035341:Telomeric Repeat Binding Protein 2; D004247:DNA; D020827:rap1 GTP-Binding Proteins
keywords: DNA curtains; Rap1; TRF1; TRF2; diffusion; electron microscopy; shelterin; single-molecule imaging; target search; telomere