Emerging accessibility patterns in long telomeric overhangs

Area of Science:

• Molecular Biology
• Biophysics
• Genetics

Background:

• Human telomeres protect chromosome ends and consist of repetitive sequences.
• Telomeric overhangs can form G-quadruplex (GQ) structures, influencing telomere function.
• The accessibility of these overhangs is critical for telomere maintenance and protection by shelterin proteins.

Purpose of the Study:

• To investigate the accessibility of human telomeric overhangs with varying lengths and GQ structures.
• To understand how overhang length and folding landscape influence accessibility patterns.
• To correlate accessibility with the stability and folding frustration of G-quadruplex structures.

Main Methods:

• Employed single-molecule FRET-PAINT experiments using a peptide nucleic acid probe.
• Studied 25 different telomeric overhangs with 4-28 repeats of the GGGTTA sequence.
• Developed a computational model to analyze folding stabilities and cooperativities of G-quadruplexes.

Main Results:

• Observed periodic changes in overhang accessibility correlated with the number of G-Tract repeats.
• [4n]G-Tract overhangs exhibited broader accessibility, while [4n+2]G-Tract overhangs showed narrower accessibility patterns.
• The junction between single- and double-stranded telomeres was found to be the least stable and most accessible region.

Conclusions:

• Folding frustration is higher in [4n]G-Tract constructs compared to [4n+2]G-Tract constructs.
• The telomeric overhang junction is a key accessible site for protein interactions.
• Findings are significant for understanding the assembly of the POT1/TPP1 and shelterin protein complex at telomeres.