Electrical Control of a Kinesin-Microtubule Motility using a Transparent Functionalized-Graphene Substrate

Abstract

Motor proteins such as kinesin and myosin generate a force to perform mechanical works and transport a cargo in cells by interacting with cytoskeletal filaments such as microtubules and actin filaments. For example, kinesin-microtubule systems convert chemical energy into mechanical works via hydrolysis of adenosine triphosphate (ATP) with a high fuel efficiency and generate a large force of ~6 pN. With development of in-vitro assays for motor proteins, motor proteins have been drawing attention as a key component for highly-efficient nano-transportation systems. For applying the biomotors on a nano-transportation system, it is important to control the motility of the motor protein. Microfabricated channels, chemical patterning, and electric forces have employed for the spatial or temporal control over kinesin-driven microtubule motility. Especially, electric fields have been studied as a means to regulate the gliding motility of microtubules driven by kinesin. However, most of previous methods relied on non-transparent electrodes as a substrate for motility assay, which is not compatible with common motility assay set-up based on transparent glass substrates and transmission fluorescence microscopes. Graphene can be a promising substrate for solving this problem due to its high transparency as well as biocompatibility, good conductivity, and high flexibility. However, the assay of kinesin-driven microtubule motility on graphene has not been reported yet. Herein, I demonstrated the electrical control of microtubule translocation propelled by kinesin using a microfabricated channel on a functionalized graphene electrode which has a high transparency and conductivity. In this strategy, graphene surface was first functionalized with a hydroxyl-terminated molecular layer to enhance the kinesin-microtubule motility on it. Then ring-shaped polymer patterns were fabricated on the functionalized graphene substrate to localize electric fields in a specific region on the graphene. When a positive bias voltage was applied to the graphene, negatively-charged microtubules were localized on the ring-shaped exposed graphene region. As a proof of concepts, I demonstrated the repeated trap-and-release events of microtubules at specific area on the graphene substrate by switching on and off the voltage. This result was the first demonstration of the motility of kinesin-microtubule on the functionalized-graphene and the real-time control of biomotor motility on the graphene-based control channel. My work shows that transparent and conducting graphene electrodes allow us to control and observe the motion of microtubules simultaneously, and they can be utilized for basic research on biomotors and various applications such as nano-transport systems.