Wednesday, October 18, 2017 at 4:00pm to 5:00pm
Physical Sciences Building, 120
245 East Avenue
Sabrina Leslie, McGill University
Host: Rob Thorne
How Biomolecules Behave in a Squeeze
How biomolecules behave in a squeeze – whether in response to confining walls or crowding agents, or inherent to particular molecular topologies, such as supercoiled DNA – presents an open and fascinating territory of exploration of the molecular machineries in living cells. In this talk, we use new microscopy tools to squeeze molecules in nanoscale containers, where we directly visualize the elusive interactions between specific unwinding sites on supercoiled DNA, and site-specific probes designed to bind to these sites, as a function of DNA supercoiling, temperature, and geometric conditions. Throughout our wide-field observations of single-molecule binding and diffusive trajectories, which extend over several seconds to minutes, the DNA molecules are free to explore all possible configurations, which we show has crucial influence over the observed dynamics. The increase in binding rate that we observe, with both temperature and supercoiling, is consistent with higher order structures in DNA (such as Z-DNA) playing a key role in governing the binding dynamics. This alternate structure suppresses supercoil-induced DNA unwinding in DNA at low temperatures, for a wide range of negative superhelicities. Beyond topology-mediated DNA interactions, the single-molecule techniques that we present may be used to visualize a wide range of molecular interactions that are challenging or impossible to access with other methods such as optical or magnetic tweezers, especially under confined and complex conditions of biological interest.