The Lawnmower: An Autonomous Synthetic Protein Motor

Abstract

Biological motors are involved in various cellular processes such as intracellular transport, DNA replication and cell motility. These examples involve multi-subunit proteins which transduce chemical energy into mechanical work. To understand better the underlying principles by which biological motors operate, it is instructive to study simpler motors which use Brownian diffusion coupled with asymmetry in the system to bias the direction of motion.Here, we describe the design and construction of a novel protein-based synthetic motor, the “lawnmower”, which uses a burnt-bridges mechanism to autonomously and diffusively move forward. The blades of the lawnmower are proteases bound to a quantum dot hub that interact with a one dimensional peptide substrate track via binding to and cleavages of the substrates. Simulations have suggested how the number of blades affects the motor properties: too many able to simultaneously bind the track means very slow motion; too few and the motor has low processivity [Samii et al., Physical Reveiw E, 84, 031111 (2011)]. In our design, cleavage of substrate by a protease releases a quencher molecule at one end of the peptide resulting in increased fluorescence of the DNA-bound product. Increased fluorescence thus acts as an indicator of the processivity of the lawnmower along the peptide track, which can be correlated to the motion of the lawnmower. This correlation provides an assessment of the directionality and processivity of our molecular motor and insight into its mechanochemical coupling. Experimentally, we confirm with kinetic assays that our lawnmower is active and that there are an average number of 8 blades on the each motor. We also demonstrate the synthesis and characterization of a highly modified DNA-peptide construct, which acts as the track for the motor.