Poster abstracts

Poster number 15 submitted by Hamza Balci

Single Molecule Investigations of Telomere Accessibility and Protection by Shelterin

Hamza Balci (Physics Department, Kent State University), Sajad Shiekh, Sineth Kodikara, John Portman (Physics Department, Kent State University), Amanda Jack, Ahmet Yildiz (Department of Molecular and Cell Biology, University of California, Berkeley)

Abstract:
We measured the accessibility and folding patterns of telomeric overhangs of physiologically relevant lengths (up to 28 GGGTTA repeats) in the absence and presence of shelterin complex using single molecule methods. In the absence of shelterin, the accessibility patterns have a well-defined periodicity with varying overhang length and show the junction region between single stranded and double stranded telomeres (ssTEL and dsTEL) to be the most accessible region of the overhang. We complemented these experiments with a computational model that correlates the accessibility patterns to folding stability, cooperative folding, and folding frustration of the G-quadruplexes that form in the overhang. Shelterin significantly (~5-fold) reduces the overall accessibility of the overhang, including the critical junction region. Using single molecule fluorescence methods (smFRET, FRET-PAINT, and PIFE), we identified the binding sites of shelterin proteins on dsTEL and ssTEL in the junction region and established the minimum length requirements for creating a protein-mediated bridge across the junction. These studies have significant implications for regulating the access of DNA-processing enzymes and DNA-binding proteins that target telomeric overhangs.

References:
Sajad Shiekh, Darion Feldt, Amanda Jack, Sabaha Pasha, Ahmet Yildiz, Hamza Balci, "Protection of Telomeric Junction by Shelterin". Manuscript in preparation

Sajad Shiekh, Amanda Jack, Ayush Saurabh, Golam Mustafa, Sineth G Kodikara, Prabesh Gyawali, Mohammed Enamul Hoque, Steve Pressé, Ahmet Yildiz, Hamza Balci, "Shelterin reduces the accessibility of telomeric overhangs", Nucleic Acids Research (2022).

Sajad Shiekh, Golam Mustafa, Mohammed Enamul Hoque, Eric Yokie, John J. Portman, Hamza Balci, "Emerging Accessibility Patterns in Long Telomeric Overhangs", PNAS (2022) https://doi.org/10.1073/pnas.2202317119

Keywords: Telomere, G-quadruplex, Shelterin