Bacterial cell division

Bacterial cell division

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Even though we probably have a complete list of proteins involved in bacterial cell division, how these molecular players are able to self-organize into a functional machinery at the right place and time is not clear.

In this research direction, we are aiming to understand the mechanism of bacterial cytokinesis by rebuilding the cell division machinery from purified components

Recently, we have used our in vitro reconstitution approach to answer the following questions: 

How do FtsZ associated proteins modulate the organization of FtsZ filaments?
The Z-ring has long been known to act as a dynamic scaffold for the assembly of the bacterial cell division machinery. What governs the architecture, dynamics and stability of this cytoskeletal structure was unclear, but FtsZ-associated proteins (Zaps) had been suggested to play an important role. We used in vitro reconstitution to study the influence of the well-conserved protein ZapA on the self-organization of FtsZ and FtsA on lipid membranes. Combining high-resolution fluorescence microscopy with novel quantitative image analysis (Caldas et al., 2020), we found that ZapA aligns FtsZ filaments and stabilizes filament bundles in a highly cooperative manner. Despite its strong influence on their large-scale organization, we found that ZapA binds only transiently to FtsZ filaments and has no effect on their treadmilling velocity. Our results led to a new model for how FtsZ-associated proteins can increase the precision and stability of bacterial cell division. Furthermore, we propose that the ultrasensitive response of FtsZ filaments to ZapA is important for the directional maturation of the cell division machinery (Caldas et al., 2019).

FtsZ-associated proteins alter the architecture and reorganization dynamics of FtsZ filaments. In the presence of ZapA, FtsZ filaments form persistent, large-scale bundles. Dual-color TIRF microscopy movie of proteins on supported membranes.

How do treadmilling FtsZ filaments organize cell division proteins in space and time?
The Z-ring not only defines the site of cell division, treadmilling of FtsZ filaments in this structure was also found to actively distribute cell wall synthesis around the cell thereby promoting the integrity of the new formed cell poles (Yang et al., 2017; Bisson-Filho et al., 2017). To understand how FtsZ filament dynamics are coupled to cell wall synthesis, we reconstituted part of the bacterial cell division machinery using its purified components FtsZ, FtsA and truncated transmembrane proteins essential for cell division (Baranova et al., 2020). We found that the membrane-bound cytosolic peptides of FtsN and FtsQ co-migrated with treadmilling FtsZ-FtsA filaments. Remarkably, despite their directed motion on the ensemble level, individual peptides showed random diffusion and transient confinement. Our findings reveal that divisome proteins dynamically follow treadmilling FtsZ filaments by a diffusion-and-capture mechanism, which can help to establish a moving signaling zone at the division site in vivo. This work represents an important experimental demonstration for how transient interactions can lead to the self-organization of complex biological structures.

Treadmilling filaments of FtsZ (left) organize the membrane anchor FtsA (middle) as well as the cytoplasmic peptide of FtsN (right) attached to the lipid bilayer. Single-molecule imaging reveals the dynamic behavior of the three different proteins on the membrane surface.

Current projects

Currently, we are using our in vitro reconstitution approach to answer the following questions:

  1. How do treadmilling FtsZ filaments distribute cell division proteins? 
  2. How do FtsZ filaments laterally interact to form a coherent structure?
  3. How does FtsA interact with other cell division proteins? 
People working on this project

Philipp, Marko, Lukas

Relevant publications

N. Baranova, P. Radler, V. M. Hernandez-Rocamora, C. Alfonso, M. Lopez-Pelegrin, G. Rivas, W. Vollmer, M. Loose.
Diffusion and capture permits dynamic coupling between treadmilling FtsZ filaments and cell division proteins.
Nature Microbiology (2020), vol. 5(3):407-417.

P. Caldas, M. Lopez-Pelegrin, D.J.G. Pearce, N.B. Budanur, J. Brugues and M. Loose. 
Cooperative Ordering of Treadmilling Filaments in Cytoskeletal Networks of FtsZ and Its Crosslinker ZapA.
Nature Communications (2019), vol. 10 (1), 5744.

Paulo Caldas, Philipp Radler, Christoph Sommer and Martin Loose. 
Computational analysis of filament polymerization dynamics in cytoskeletal networks. 
Methods in Cell Biology (2020), vol. 158:145-161.

Funding

This research project has received funding from the European Research Council (ERC) with a ERC Starting Grant (“Self-organization of the bacterial cell”, Grant No. 679239).