Cell-Space Confinement Effects on Min Protein Waves Inside Microdroplets

Abstract

Min system is the determinant mechanism of the position of division plane in bacterial cells. Reaction-diffusion coupling of Min system components (MinD, MinE, and ATP) emerges pole-to-pole oscillation of Min proteins (Min wave), and it inhibits assemblies of cell division initiator (Z ring) except at the center of cell. Although Min wave has been successfully reconstituted on 2D planar membrane and in fully confined systems, we found that physiological concentration of Min system components does not emerge Min wave in microdroplets covered with E. coli polar lipids. This finding is contrary to the results from previous studies, and thus, we investigated the mechanism underlying this difference.Consequently, we found “cell-space confinement effects” are the cause of the difference. Recent studies have shown that “cell-space confinement effects” changes behaviors and dynamics of biological systems. In the case of Min system, our biochemical investigations showed that the cell-space confinement changes physicochemical parameters of Min proteins, and hence, behaviors of Min wave were altered by the confinement. Furthermore, we showed a macromolecular crowding reagent counteract the change of the physicochemical parameters of Min proteins, and ensure stable emergence of Min wave inside microdroplets covered with E.coli polar lipids. We also found that artificial lipid composition of the previous study using microdroplets works similarly to the macromolecular crowding reagent we used.Our results predict that undefined factors are critical for stable emergence of Min wave in living cells, and evoke that importance of cell-size confinement effect for understanding coupling of reaction with diffusion in living systems.