Bacterial division FtsZ forms liquid condensates with nucleoid-associated Z-ring inhibitor SlmA

Abstract

17Macromolecular condensation resulting from biologically regulated liquid-liquid phase 18 transitions is emerging as a mechanism to organize the intracellular space in 19 eukaryotic systems, with broad implications in cell physiology and pathology. Here we 20 show that FtsZ, central element of the division ring in most bacteria, forms condensates 21 when in complex with SlmA, the protein preventing septal ring assembly nearby the 22 chromosome in E. coli. The formation of condensates is promoted by crowding and 23 enhanced by sequence-specific binding of SlmA to DNA. These structures are dynamic 24 and FtsZ within them remains active for GTP-triggered fiber formation. Their location is 25 sensitive to compartmentalization and to the presence of a membrane boundary in 26 microfluidics-based cell mimetic systems, likely affecting their reactivity. We propose 27 that reversible condensation may play a role in the modulation of FtsZ assembly and/or 28 location by SlmA and, hence, in the regulation of ring stability, constituting a singular 29 example of a prokaryotic nucleoprotein complex exhibiting this kind of phase transition.30 31 32 33 34 35 36 Recent studies evidence the relevance of the transient condensation of proteins and 37other molecules into structures behaving as liquid droplets in the spatiotemporal 38 regulation of biological processes [1]. The emergence of these membraneless 39 compartments can be described as a liquid demixing process generating phase 40 boundaries to temporarily confine specific functional entities [2]. The selective 41 accumulation of biomolecules in these dynamic compartments may deeply influence 42 their reactivity, enhancing and accelerating their mutual recognition while disfavoring 43 interactions with excluded elements [3][4][5]. Crowding due to the overall high 44 concentration of macromolecules in the cells clearly provides a non-specific driving 45 force favoring phase transitions and condensation [6-10], another contributing factor 46 being, it seems, multivalency [1, 3, 11, 12]. Indeed, most biomolecular condensates 47 analyzed consist of various molecules containing multiple homo or heteroassociation 48 elements, like nucleic acids, usually RNA, and proteins harboring various domains of 49 interaction [1]. The presence of unstructured regions in proteins also seems to promote 50 condensation and a number of intrinsically disordered proteins have been found to form 51 liquid droplets on their own under crowding conditions in vitro and in vivo that evolve 52 towards solid aggregates [9, 10,[13][14][15]. Specific features shared by these 53 condensates, like the ability to exchange molecules with the surroundings, their local 54 and reversible generation in response to changes in component interactions and/or 55 concentrations, and their evolving physical properties [1] make them particularly 56 suitable for the fine tuning of molecular localization and reactivity. 57 Phase separation has been shown to occur in a variety of signaling and other systems 58 in eukaryotes (s...

The bacterial DNA binding protein MatP involved in linking the nucleoid terminal domain to the divisome at midcell interacts with lipid membranes

“…Examples of these proteins are the nucleoid occlusion Noc from Bacillus subtilis (14), a negative modulator of Z-ring assembly, and SeqA from E. coli , a protein involved in the sequestration of replication origins (24). Along the same line, the nucleoprotein complexes of SlmA, the factor counteracting Z-ring formation around the chromosome in E. coli , seem to be brought close to the membrane (4, 25, 26), possibly through transertional linkages (25) and/or biomolecular condensation (27). Conversely, well-known membrane associated proteins like MinD from the Min system (28) have also been shown to interact, in a non-sequence specific manner, with chromosomal DNA (13).…”

FtsZ‐Induced Shape Transformation of Coacervates

“…In comparison, the possibility of FtsZ to interact with membrane‐less coacervates is largely unexplored. A recent in vitro work has shown that FtsZ forms coacervates with SlmA, a protein involved in the inhibition of the septal ring assembly in the vicinity of chromosomes. However, it remains to be seen whether FtsZ has the ability to dynamically interact with membrane‐less condensates, possibly leading to morphological changes to them, as is the case with membrane‐bound containers.…”

Regulation of a bacterial histidine kinase by a phase separating scaffolding protein

“…4-5), phase separate as two distinct membraneless organelles at opposite ends of the cell. In addition, several other recent studies have shown that bacteria leverage phase separation to compartmentalize and regulate RNA polymerase 42 , mRNA decay 43,44 , ABC transporters 45 , DNA repair 46 , cell division 47 , chromosome segregation 48 and carboxysome assembly 49. These studies have laid the foundation to consider the extent and advantages of organizing biochemistry within biomolecular condensates in the bacterial cytoplasm.…”