Physics & Astronomy Nate Derr - Smith College

"Investigating the Collective Motility of Dynein Motor Ensembles Using Structural DNA Nanotechnology"

Kinesin and cytoplasmic dynein are microtubule-based motors that drive intracellular cargo transport in eukaryotic cells. Many intracellular cargos are propelled by small groups of these motors working in ensembles. Yet many of the biophysical mechanisms that govern ensemble motility remain unknown. Building upon our previous work using the techniques of DNA origami (Derr & Goodman et al Science 2012), we have designed a programmable synthetic cargo “chassis” that allows us to control both the number of motors in the ensemble and the rigidity of the cargo chassis that links them. On this chassis, motors within an ensemble are conjugated together through variable length cargo “linker” regions comprised of parallel instances of either single- or double-stranded DNA. The configuration of these regions control the number of independent steps each motor can take before exerting forces on the other motors within the ensemble. This design enables us to investigate how the “communication" of motor stepping through the cargo structure affects interactions within the ensemble and how multiple linked, but independently acting, motors can coordinate to haul cargo. Using TIRF microscopy, we have observed dynein ensembles in vitro transporting these cargo chassis along microtubules. In contrast to our previous results using a rigid chassis (Derr & Goodman et al Science 2012) we find that ensembles of dynein on non-rigid cargos move faster as more motors are added. Our results suggest that cargo rigidity, and the ability for motors to communicate their steps to one another, play important roles in determining the collective motility of multiple molecular motors.