Geometry sensing by self-organized protein patterns

Abstract

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. Despite the possibility to reconstitute protein selforganization with only a few purified components, we still lack knowledge of how geometrical boundaries affect spatiotemporal protein patterns. Following a minimal systems approach, we used purified proteins and photolithographically patterned membranes to study the influence of spatial confinement on the self-organization of the Min system, a spatial regulator of bacterial cytokinesis, in vitro. We 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. Using a computational model we quantitatively analyzed our experimental findings and identified persistent binding of MinE to the membrane as requirement for the Min system to sense geometry. Our results give insight into the interplay between geometrical confinement and biochemical patterns emerging from a nonlinear reaction-diffusion system. in vitro reconstitution | microstructures | supported lipid bilayers | spontaneous protein waves | Min oscillations P attern formation is one of the most intriguing features of biological systems. It takes place on many different spatial and temporal scales and several levels of complexity (1). Inside of the living cell, nonlinear reaction-diffusion dynamics allow proteins to encode for positional information (2-5), required to coordinate complex processes like cell division (6, 7), cell motility (8, 9), or give rise to information flow within the cell (5, 10). In reverse, cell geometry presumably affects such protein patterns, allowing processes within the cell to respond to changes in cell size and shape (11). However, how these reaction-diffusion systems sense the shape and the dimensions of the cell remains an outstanding question and requires decisive experimental testing.A well-studied example for a biochemical reaction-diffusion process is the spatiotemporal oscillations of the Min proteins in Escherichia coli (12, 13). The Min system positions the division septum in the cell to its center, such that it divides into two equally sized daughter cells. Oscillations emerge from the interactions of two proteins and the cytoplasmic membrane (14-16): MinD, a membrane-binding ATPase, and MinE, the activator of ATP hydrolysis and thus, antagonist of MinD in its membranebound state. In vivo, the intrinsic wavelength of Min protein oscillations is similar to the size of the E. coli cell, about 5 μm versus 3 μm cell length and 1 μm cell diameter (17). The ability of the Min system to sense the enclosed volume of the bacterial cell has been demonstrated in E. coli cells, which lost th...

Protein Patterns and Oscillations on Lipid Monolayers and in Microdroplets

“…Previously, we have reconstituted the pole‐to‐pole oscillations of the Min proteins, as well as their ability to spatially direct FtsZ‐mts (FtsZ fused to a membrane‐targeting sequence)16 to the middle of a microfabricated compartment 12, 17. However, although the cell membrane of E. col i is a closed compartment, Min oscillations have thus far only been successfully reconstituted in volumes not fully enclosed by membranes, but open at least at one site 12, 18, 19. Moreover, although membrane‐attached FtsZ rings have been observed in vesicles16, 20, 21 and FtsZ bundles have been characterized in the lumen of droplets,22 we are just beginning to understand how systems parameters, such as compartment geometry, influence FtsZ ring structure and dynamics.…”

Effective 2D model does not account for geometry sensing by self-organized proteins patterns

“…By means of a computational model analysis accompanying intriguing experiments, Schweizer et al (1) claim to show that MinE membrane binding is responsible for selforganized geometry sensing.…”

Divided we stand: splitting synthetic cells for their proliferation

“…Importantly, the E. coli Min system was reconstituted in an in vitro assay both on a planar supported lipid membrane (SLB) (Loose et al 2008(Loose et al , 2011Schweizer et al 2012) and recently in micro-cavities (see Fig. 6a) (Zieske and Schwille 2013;Caspi et al 2014, to be published).…”