Bacterial FtsZ protein forms phase‐separated condensates with its nucleoid‐associated inhibitor SlmA

Abstract

Macromolecular condensation resulting from biologically regulated liquid–liquid phase separation is emerging as a mechanism to organize intracellular space in eukaryotes, with broad implications for cell physiology and pathology. Despite their small size, bacterial cells are also organized by proteins such as FtsZ, a tubulin homolog that assembles into a ring structure precisely at the cell midpoint and is required for cytokinesis. Here, we demonstrate that FtsZ can form crowding‐induced condensates, reminiscent of those observed for eukaryotic proteins. Formation of these FtsZ‐rich droplets occurs when FtsZ is bound to SlmA, a spatial regulator of FtsZ that antagonizes polymerization, while also binding to specific sites on chromosomal DNA. The resulting condensates are dynamic, allowing FtsZ to undergo GTP‐driven assembly to form protein fibers. They are sensitive to compartmentalization and to the presence of a membrane boundary in cell mimetic systems. This is a novel example of a bacterial nucleoprotein complex exhibiting condensation into liquid droplets, suggesting that phase separation may also play a functional role in the spatiotemporal organization of essential bacterial processes.

Phase separation by ssDNA binding protein controlledviaprotein-protein and protein-DNA interactions

“…All in all, along with the few recently discovered cases of bacterial LLPS (Al-Husini et al, 2018;Heinkel et al, 2019;Monterroso et al, 2019), our findings highlight that LLPS is a fundamental, universally exploited mechanism that is governed by similar molecular mechanisms in bacteria and eukaryotes. The LLPS propensity predicted for human SSB homologs hSSB1/SOSB1 and hSSB2/SOSB2 suggests broad evolutionary conservation of this feature (Fig.…”

“…Whereas LLPS seems to be a heavily exploited process in eukaryotes and viruses (Heinrich et al, 2018;Nikolic et al, 2017Nikolic et al, , 2018Zhou et al, 2019), up until today only a few bacterial proteins were reported to undergo LLPS. These include Caulobacter crescentus Ribonuclease E (RNase E) that orchestrates RNA degradosomes (Al-Husini et al, 2018), Escherichia coli (E. coli) FtsZ that forms the division ring during cell divisions (Monterroso et al, 2019) and Mycobacterium tuberculosis Rv1747 that is a membrane transporter of cell wall biosynthesis intermediates (Heinkel et al, 2019). All in all, the hitherto accumulated observations imply that LLPS is a fundamental mechanism for the effective spatiotemporal organization of cellular space, with emerging but hardly explored functions in bacteria.…”

Dynamic Synthetic Cells Based on Liquid–Liquid Phase Separation

“…[150] In one recent example, FtsZ proteins were shown to undergoa ssociativeL LPS when mixed with the DNA-binding small aggregate formation protein (SmlA) under crowding conditions, producing droplets capable of reversible evolution to fibres in the presence of guanosine triphosphate (GTP). [151] Spontaneous sequestration of actin filaments in PEGsuspended dextran-rich microdroplets was also reported, and the accumulation of bundled filaments at the droplets urface was shown to induce dropletdeformations. [58] Cytoskeletonr econstitution has also been investigated in dropletsf ormed by associative phase separation.…”

Biomolecular condensates in neurodegeneration and cancer

“…Cell type‐specific condensates mediate specialized functions in different cells such as germ specification and neurotransmitter receptor clustering (Figure , green condensates) . Emerging evidence indicates that diverse biomolecular condensates also exist in prokaryotes, regulating processes such as RNA degradation and organization of DNA and the cytoskeleton . Thus, biomolecular condensates are an evolutionarily conserved means of organizing molecules and reactions.…”