Single-particle tracking method for quantitative tracking and biophysical studies of the MinE protein

Abstract

The dynamics of the MinE protein has been recognized to play an important role in accurate placement of the septum during cell division. The system is of great interest because it represents one of the few biologically self-sustaining oscillatory systems in an organism that can be well-studied at physical, generic and biochemical levels. In this work, single-particle tracking (SPT) was, for the first time, applied to investigate the MinE behavior in an E. coli system. The SPT data monitored from the dividing E. coli cells, 5.08 ± 0.82 μm in length, have demonstrated an oscillation of the MinE protein between the two poles with an average period of 266.64 ± 122.29 seconds. The results for the oscillating trajectory and velocity can be classified according to the space and time scales of dynamic events into two types: flight events and switching events. The switching events mostly occur near polar zones while the flight events take place between the switching events in the space between the polar zones. From quantitative analysis, we found the flight events to occur with an average flight velocity of 0.23 ± 0.08 μm/s and the flight events to occur during turning at the poles with an average switching velocity of 2.16 ± 0.68 μm/s. The agreements between our findings and those from previous studies are discussed. These results demonstrate the benefits of applying SPT to investigate the oscillations of targeted proteins in both qualitative and quantitative ways. The emphasis of this report is not on discovering biophysical information but on providing a new methodology to obtain information that will be essential to evaluate the many mathematical models that have been proposed to account for the Min protein oscillation system.