title: G-register exchange dynamics in guanine quadruplexes.
abstract: G-quadruplexes (GQs) are 4-stranded DNA structures formed by tracts of stacked, Hoogsteen-hydrogen bonded guanosines. GQs are found in gene promoters and telomeres where they regulate gene transcription and telomere elongation. Though GQ structures are well-characterized, many aspects of their conformational dynamics are poorly understood. For example, when there are surplus guanosines in some of the tracts, they can slide with respect to one another, a process we term G-register (GR) exchange. These motions could in principle entropically stabilize the folded state, crucially benefitting GQs as their stabilities are closely tied to biological function. We have developed a method for characterizing GR exchange where each isomer in the wild-type conformational ensemble is trapped by mutation and thermal denaturation data for the set of trapped mutants and wild-type are analyzed simultaneously. This yields GR isomer populations as a function of temperature, quantifies conformational entropy and sheds light on correlated sliding motions of the G-tracts. We measured entropic stabilizations from GR exchange up to 14.3 ± 1.6 J mol(-1) K(-1), with melting temperature increases up to 7.3 ± 1.6°C. Furthermore, bioinformatic analysis suggests a majority of putative human GQ sequences are capable of GR exchange, pointing to the generality of this phenomenon.
authors.affiliation: McGill University, Department of Chemistry, 801 Sherbrooke St. West, Montreal, QC H3A 0B8, Canada.
authors.forename: Robert W
authors.initials: RW
authors.lastname: Harkness
authors.affiliation: McGill University, Department of Chemistry, 801 Sherbrooke St. West, Montreal, QC H3A 0B8, Canada anthony.mittermaier@mcgill.ca.
authors.forename: Anthony K
authors.initials: AK
authors.lastname: Mittermaier
mesh_terms: D001483:Base Sequence / Q000235:genetics; D002942:Circular Dichroism; D004247:DNA / Q000737:chemistry*; D054856:G-Quadruplexes; D006151:Guanosine / Q000737:chemistry*; D006801:Humans; D009154:Mutation / Q000235:genetics; D019906:Nuclear Magnetic Resonance, Biomolecular; D011401:Promoter Regions, Genetic / Q000235:genetics; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics*; D051573:Proto-Oncogene Proteins c-pim-1 / Q000235:genetics*; D013816:Thermodynamics; D014158:Transcription, Genetic / Q000235:genetics; D042461:Vascular Endothelial Growth Factor A / Q000235:genetics*
chemical_list: C489427:MYC protein, human; D016271:Proto-Oncogene Proteins c-myc; C467484:VEGFA protein, human; D042461:Vascular Endothelial Growth Factor A; D006151:Guanosine; D004247:DNA; C496634:PIM1 protein, human; D051573:Proto-Oncogene Proteins c-pim-1