Study of Min Protein-Induced Membrane Waves in vitro

Abstract

In the bacterium Escherichia coli, the proper placement of the division site selection is regulated in part by the pole-to-pole oscillations of Min proteins. In vitro, the oscillation dynamics emerges from the self-organization of MinD, MinE and ATP. However, it is still not clear how the Min proteins affect the E. coli lipid membrane and directly interact with other E. coli proteins. We hypothesized that the spatial oscillations of Min protein systems could play a crucial role in changing lipid membrane dynamics and therefore influence other membrane species indirectly. We developed supported E. coli lipid bilayer platforms in order to systematically explore the underlying mechanism between membrane and Min proteins. We observed spiral membrane waves on fluorescence-labeled E. coli membrane platforms after we introduced unlabeled MinD, MinE and ATP to the membrane. Fluorescence recovery after photobleaching (FRAP) technique was used to study the membrane pattern dynamics. We found that dynamics of the membrane waves had different characteristics from those of the Min protein waves by Kymograph analysis. The simultaneous observation of the labeled Min proteins and the labeled membranes further suggested that the membrane pattern dynamics was directly influenced by the binding concentration gradients of the Min proteins. We will further incorporate some E. coli signaling proteins into the membrane to examine whether their movement or clustering can be influenced by the Min proteins-induced membrane pattern. The result could provide us insights into the long-standing question about the possible function of the E. coli Min protein oscillation phenomenon.Keywords: Min system, self-organization, supported lipid bilayers, dynamic patterns