Title: An SSDNA Based Force Sensor for Multi Motor Transport as an Alternative to Optical Tweezers
Abstract: Forces exerted by molecular motors have traditionally been quantified by optical tweezers. The requirement of physical connection to microscopic beads and low-throughput in an optical tweezer experiment limits its applicability in diverse configurations. We present a single-stranded DNA-based force sensor that can measure forces exerted by individual molecular motors in real-time when multiple motors are transporting a common microtubule. An ssDNA molecule, which acts as a force sensing molecule, is sandwiched between motor molecules and the coverslip. We demonstrate the applicability of our sensor in the multi-kinesin-based microtubule transport. We find that kinesin motors exert less than 1 pN force while collectively transporting a microtubule, and they add together in small but significant ways. We also perform our assay in the presence of varying sizes of roadblocks. Kinesin motors modulate their forces upon encountering the roadblocks. However, forces by kinesin remain below 1 pN, much below the stall force of 7 pN. We speculate that the kinesins detach briefly upon encountering a roadblock while having other kinesins in the team prevent the kinesins from drifting away. Our assay is high-throughput and can be used for other types of motors such as dynein and myosin.