Assembly of bacterial cell division protein FtsZ into dynamic biomolecular condensates

Abstract

Biomolecular condensation through phase separation may be a novel mechanism to regulate bacterial processes, including cell division. Previous work revealed FtsZ, a protein essential for cytokinesis in most bacteria, and the E. coli division site selection factor SlmA form FtsZ∙SlmA biomolecular condensates. The absence of condensates composed solely of FtsZ under the conditions used in that study suggested this mechanism was restricted to nucleoid occlusion or SlmA-containing bacteria. Here we report that FtsZ alone can demix into condensates in bulk and when encapsulated in synthetic cell-like systems. Condensate assembly depends on FtsZ being in the GDP-bound state and on crowding conditions that promote its oligomerization. FtsZ condensates are dynamic and gradually convert into FtsZ filaments upon GTP addition. Notably, FtsZ lacking its C-terminal disordered region, a structural element likely to favor biomolecular condensation, also forms condensates, albeit less efficiently. The inherent tendency of FtsZ to form condensates susceptible to modulation by physiological factors, including binding partners, suggests that such mechanisms may play a more general role in bacterial cell division than initially envisioned.

FtsZ Interactions and Biomolecular Condensates as Potential Targets for New Antibiotics

“…Phase separation could be caused by the multivalent interactions established by these proteins, enhanced by crowding and by the presence of the DNA sequences targeted by SlmA. In the absence of SlmA, FtsZ by itself can achieve a sufficiently dense network of interactions to phase separate, but only at high magnesium and low potassium concentrations ( Figure 2 ) [ 43 ]. Both the homotypic and heterotypic FtsZ condensates described so far involve the GDP form of the protein, which is still active for polymerization when GTP is added to the condensates.…”

“…Both the homotypic and heterotypic FtsZ condensates described so far involve the GDP form of the protein, which is still active for polymerization when GTP is added to the condensates. A putative role of condensates in the regulation of FtsZ spatial distribution and function, and ultimately in the mechanism leading to division in normal bacteria, has been suggested [ 42 , 43 ]. It has also been hypothesized that the reversible formation of these condensates could respond to stress signals.…”

“…The assays so far developed to study FtsZ biomolecular condensates would help to identify such candidates. Confocal fluorescence microscopy imaging has been an invaluable tool for the identification and characterization of FtsZ biomolecular condensates in crowding solutions in bulk and in cytomimetic systems [ 42 , 43 ]. In those studies, confocal microscopy measured the size and shape of condensates formed by the scaffold biomolecules.…”

“…Those studies also measured turbidity over time, which provided more quantitative information about the factors affecting condensate formation and permitted simultaneous evaluation of dozens of samples using a plate reader. Parallel measurements by confocal imaging and turbidity provided valuable information about how crowding, protein and nucleic acid concentration, salt and divalent cations fine tune condensate assembly by FtsZ [ 42 , 43 ].…”

“…Formation of these condensates is facilitated by the interactions between FtsZ and its antagonist SlmA, which itself is bound to DNA. FtsZ can also form these condensates on its own ( Figure 2 ), albeit less efficiently [ 43 ]. The assembly of biomolecular condensates arising from phase separation is emerging as a new mechanism for the spatial organization of biomolecules to optimize their function [ 44 ].…”