LMP Seminar: Nonequilibrium transport phenomena induced by conformational changes of biological nanomachines

In this seminar, I will talk about the effects of conformational changes on the nonequilibrium transport phenomena in living systems. First, I discuss the hydrodynamic collective effects due to active protein molecules that are immersed in lipid bilayer membranes and modeled as stochastic force dipoles. Using the generalized membrane mobility tensors, I estimate the active diffusion coefficient and the drift velocity as a function of the size of a diffusing object. It is shown that the competition between the thermal and nonthermal contributions in the total diffusion coefficient is characterized by two length scales corresponding to the membrane geometries. In addition, rheological properties of active protein solutions will be discussed. Next, I focus on the biological membrane with rotatory proteins and investigate its active chiral properties by introducing odd viscosity. It is known that this transport coefficient exists only when the time-reversal and parity symmetries are broken. Considering the difference in odd viscosity between the inside and outside of the liquid domain, I analytically obtain the forces on the domain moving in a 2D fluid. In contrast to the passive case without odd viscosity, the lateral lift force arises in the active case only when the in/out odd viscosity is different. Moreover, I discuss the forces acting on a rigid disk in a compressible fluid by generalizing the Lorentz reciprocal theorem for a 2D fluid with finite odd viscosity.