Biophysical Society Thematic Meeting | Tutzing 2026

Single-Molecule FRET: The Next 30 Years

Poster Abstracts

12-POS Board 6 ON CONFORMATIONAL SWITCHING OF G-QUADRUPLEX DNA Gillian Cadden 1 ; Aleksandra Bednarz 1 ; Ganesh Agam 2 ; Tim Schröder 3 ; Philip Tinnefeld 3 ; Don C Lamb 3 ; Victoria Birkedal 1 ; 1 Aarhus University, Chemistry, Aarhus, Denmark 2 University of Cambridge, MRC Laboratory of Molecular Biology, Cambridge, United Kingdom 3 Ludwig Maximilian University, Department of Chemistry and Center for NanoScience (CeNS), Munich, Germany G-quadruplexes are non-canonical nucleic acid structures formed by guanine-rich sequences found within biologically important genomic regions such as telomeres and gene promoters. Their structural polymorphism is thought to be central to their biological roles, yet the fast dynamic interconversion between folded, unfolded and intermediate states remains poorly understood. Here, we combine surface- and solution-based single-molecule FRET to investigate genomic G-quadruplex dynamics across multiple timescales. G4-forming sequences were incorporated into DNA origami platforms to extend residence times during solution measurements, enabling fast conformational dynamics to be better resolved. TIRF measurements directly captured slow K ⁺ -dependent switching between unfolded and folded conformations. Complementary confocal measurements and dynamic photon distribution analysis revealed multiple coexisting FRET states and sub-millisecond exchange between unfolded and folded/intermediate conformations, with relaxation times strongly dependent on K ⁺ concentration. Mutant telomeric constructs that prevent full G4 formation suggest that G-hairpin like intermediates contribute to the observed fast dynamics. This multi-timescale view provides new insight into how biologically relevant G-quadruplexes explore conformational states linked to their regulatory functions.

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