Enhanced electrostatic force microscopy reveals higher-order DNA looping mediated by the telomeric protein TRF2

Area of Science:

• Molecular Biology
• Biophysics

Background:

• The shelterin protein TRF2 plays a crucial role in telomere maintenance by compacting double-stranded DNA (dsDNA) and facilitating T-loop formation.
• Understanding the precise DNA pathways within TRF2-DNA complexes is essential for elucidating the mechanisms of TRF2-mediated DNA compaction.

Purpose of the Study:

• To investigate the spatial organization and path of DNA within large TRF2-DNA complexes.
• To reveal the structural basis of TRF2-mediated DNA compaction at the molecular level.

Main Methods:

• Development and application of Dual-Resonance-frequency-Enhanced Electrostatic force Microscopy (DREEM) imaging to visualize DNA location within protein-DNA complexes.
• Utilizing coarse-grained molecular dynamics simulations to model TRF2-mediated DNA compaction processes.

Main Results:

• DREEM imaging demonstrated that large TRF2-DNA complexes (exceeding TRF2 tetramer volumes) compact DNA internally, with folded DNA segments observed at the complex periphery.
• Simulations supported these findings, identifying structural requirements and sequential steps in TRF2-mediated DNA compaction, consistent with observed folded DNA structures and protruding loops.

Conclusions:

• The study reveals novel DNA paths within TRF2 complexes, distinct from chromatin structure.
• These findings provide crucial mechanistic insights into the structure-function relationships governing telomere maintenance and DNA repair pathways.