The Jun Lab

for experimental cellular biophysics and nonequilibrium physics

Understanding the collective motion of molecular motors in in vitro and in vivo


Microtubule (MT)-based motors like kinesin play important cellular roles and are essential for both long-distance transport of cargos (e.g. in axons) and also for cell division. MTs are polar (directed) filaments, and in cells, kinesin moves cargos toward the plus-end of MTs while dynein drives them toward the MT minus end. Defects in motor-based transport are closely linked to neurodegenerative diseases, including Alzheimer's and Huntington's diseases.

Long-distance transport reflects the collective behavior of the motors functioning as a team bound to cargos. Importantly, we lack a full understanding how motors work together, or how their collective function can be regulated to control the motion of vesicles in cells. This lack partly reflects the difficulty in studying the process in cells, where one cannot easily determine or control the motor number or the presence of associated regulatory factors. The recent successful efforts to characterize structures and functions of single molecular motors in vitro are a crucial first step to understanding the more complicated intracellular motion of cargos. The next step that is a focus of my long-term research is to tackle three related problems: how do multiple motors function together, which properties of single-motors are important for this function, and how are these properties regulated?

Nonequilibrium Physics using a feedback trap

We build up the feedback trap (A.K.A. ABEL trap) to study the non-equilibrium thermodynamics. Classical thermodynamics provides knowledge about energy exchange processes in a macroscopic system. In such system, entropy production is zero or increases in the process, and its fluctuations are very small. In contrast, in the small system where thermal fluctuations are dominant, entropy production can be negative, which seems a violation of the 2nd law of thermodynamics. Therefore, such small systems are not well described by classical thermodynamics. Since the 1980s, new theories, called fluctuation theorem, have been proposed to explain the dynamics of the small system and broadened thermodynamics to non-equilibrium state. Recently, many theories of connection of information to thermodynamics have been developed, and we experimentally showed that information is a real physical quantity. We will continue to focus on non-equilibrium physics such as information and entropy using the feedback trap.