Current and past research

Self-organization of the FtsA and FtsZ into dynamic cytoskeletal networks.

In bacteria, the tubulin-related GTPase FtsZ and the actin-related protein FtsA cooperate to form the Z-ring required for cytokinesis, but how they influence each other’s assembly dynamics is not known. By reconstituting their dynamics using a minimal set of components, I could show that  FtsZ and FtsA to self-organize into complex dynamic patterns, such as fast-moving filament bundles and chirally rotating rings. Using fluorescence microscopy and biochemical perturbations, I found that large-scale rearrangements of FtsZ emerge from its polymerization dynamics coupled to a dual, antagonistic role of FtsA: recruitment of FtsZ filaments to the membrane and a negative regulation on FtsZ assembly. These findings provide a new model for the initial steps of bacterial cell division and providing insights into the potential regulatory interplay of the two proteins. 

Loose and Mitchison, Nature Cell Biology (2014) 

Influence of geometry sensing of self-organized protein patterns

In the living cell, proteins are able to organize space much larger than their dimensions. In return, changes of intracellular space can influence biochemical reactions, allowing cells to sense their size and shape. I used photolithographically patterned membranes to study the influence of spatial confinement on the self-organization of the Min system in vitro. I found that the emerging protein pattern responds even to the lateral, two-dimensional geometry of the membrane such that, as in the three-dimensional cell, Min protein waves travel along the longest axis of the membrane patch. This shows that for spatial sensing the Min system does not need to be enclosed in a three-dimensional compartment. The results give insight into the interplay between geometrical confinement and biochemical patterns emerging from a nonlinear reaction-diffusion system.

Schweizer*, Loose*, et al. PNAS (2012)

Single molecule studies on Min protein waves

Using single-molecule and confocal microscopy I could elucidate the order of events during Min wave propagation. I found that protein detachment at the rear of the wave, and the formation of the E-ring, are accomplished by two complementary processes: first, local accumulation of MinE due to rapid rebinding, leading to dynamic instability; and second, a structural change induced by membrane-interaction of MinE in an equimolar MinD-MinE (MinDE) complex, which supports the robustness of pattern formation.

Loose et al., Nature Structural & Molecular Biology, (2011).

In vitro reconstitution of Min protein waves

In the bacterium Escherichia coli, the Min proteins oscillate between the cell poles to select the cell center as division site. This dynamic pattern has been proposed to arise by self-organization of these proteins, and several theoretical models have suggested a reaction-diffusion type mechanism. I found that the Min proteins can spontaneously formed planar surface waves on a flat membrane in vitro. Together with the group of Karsten Kruse, we developed a model to explain the self-organization of these protein waves.

Loose et al., Science (2008)