Parastoo Maleki, PhD
Kent State University, Department of Physics
Monday April 1, 2019 – 12PM
One of the therapeutic targets that has attracted attention in targeted therapy is guanine quadruplex (GQ), which forms in guanine-rich nucleic acid sequences, such as telomeres. Studies on cancer cells show that stabilizing the GQ structures in telomeres with small molecules reduces telomerase activity and proliferation of cancer cells. Because of their role in biological processes and their potential use as therapeutic targets, GQ structures have been utilized in characterizing the efficacy of small molecule anti-cancer drugs.
Despite the observation of enhanced thermodynamic stability imparted by such small molecules on GQ, the underlying dynamics of small molecule-GQ interactions are not known. To have a better understanding of these interactions we employed single molecule Förster resonance energy transfer (smFRET) to study the system, where we utilized a Cy5-labeled OTD (L1Cy5- 7OTD). These studies demonstrate that interactions of this small molecule with GQ are dynamic in terms of binding kinetics and possibly in terms of rotational freedom. The Cy5 fluorophore has enabled monitoring and quantifying binding, dwell, and dissociation of a single L1Cy5-7OTD molecule as it interacted with GQ, which to our knowledge has not been demonstrated for any GQ stabilizing small molecule before. We show that L1Cy5-7OTD remains bound to GQ for tens of seconds, with significantly longer dwell times and higher binding frequencies for more stable GQ.
Moreover, we study how stability of GQ against Bloom helicase (BLM) is impacted by its interactions with several prominent small molecules. We consider two different approaches to quantify this effect: dynamic approach and steady state approach. We observe significant enhancement in GQ stability in the presence of small molecules. The similarity of the results attained from the two approaches illustrates a consistent picture in terms of the impact of these molecules on BLM-GQ interactions.