Biophysical analysis of the human POT1‐TPP1 complex reveals functional protein‐protein and protein‐DNA interactions involved in telomere maintenance (926.1)

Telomeres are nucleoprotein complexes that reside at the ends of linear chromosomes. Six specialized proteins interact specifically with telomere DNA and one another to form a protective moiety called shelterin. Telomere repeat‐binding factors (TRF) 1 and 2 bind to the double‐stranded telomere DNA sequence and the Protection of telomeres 1 (POT1) protein binds to the single‐stranded DNA overhang. RAP1, TIN2, and TPP1 interact with TRF1, TRF2, and POT1 to form shelterin. TPP1, specifically, interacts with POT1 to increase its affinity and selectivity for telomere DNA. In addition, TPP1 recruits telomerase to the telomere, where it can synthesize telomere DNA. X‐ray crystallography has revealed the atomic structures of individual domains of POT1 and TPP1, but the molecular interactions between the two proteins with and without DNA remains obscure. Using amide hydrogen‐deuterium exchange and biochemical analysis, we have determined the regions of TPP1 that are responsible for POT1‐interactions and those that are altered upon DNA binding. Combining these experimental data with homology modeling allowed us to construct a model of the POT1‐TPP1‐DNA complex and interpret its biological function in DNA recognition and in regulating telomerase activity. Grant Funding Source : Supported by American Heart Association 11SDB5580010 and American Cancer Society RSG‐13‐211‐01‐DM