Szoke, T. | Search bioRxiv

bioRxiv2022

Regulation of major bacterial survival strategies by transcript sequestration in a membraneless organelle

Liquid-liquid phase separation (LLPS) of proteins was shown in recent years to regulate spatial organization of cell content without the need for membrane encapsulation in eukaryotes and prokaryotes. Yet evidence for the relevance of LLPS for bacterial cell functionality is largely missing. Here we show that the sugar metabolism-regulating clusters, recently shown by us to assemble in the E. coli cell poles by means of the novel protein TmaR, are formed via LLPS. A mutant screen uncovered residues and motifs in TmaR that are important for its condensation. Upon overexpression, TmaR undergoes irreversible liquid-to-solid transition, similar to the transition of disease-causing proteins in human, which impairs bacterial cell morphology and proliferation. Not only does RNA contribute to TmaR phase separation, but by ensuring polar localization and stability of flagella-related transcripts, TmaR enables cell motility and biofilm formation, thus providing a linkage between LLPS and major survival strategies in bacteria.

microbiology↗

bioRxiv2020

Tyrosine phosphorylation-dependent localization of TmaR, a novel E. coli polar protein that controls activity of the major sugar regulator by polar sequestration

The poles of E. coli cells are emerging as hubs for major sensory systems, but the polar determinants that allocate their components to the pole are largely unknown. Here, we describe the discovery of a novel protein, TmaR, which localizes to the E. coli cell pole when phosphorylated on a tyrosine residue. TmaR is shown here to control the subcellular localization of the general PTS protein Enzyme I (EI) by preventing it from exerting its activity by binding and polar sequestration, thus regulating sugar uptake and metabolism. Depletion or overexpression of TmaR results in EI release from the pole or enhanced recruitment to the pole, which leads to increasing or decreasing the rate of sugar consumption, respectively. Notably phosphorylation of TmaR is required to release EI and enable its activity. Like TmaR, the ability of EI to be recruited to the pole depends on phosphorylation of one of its tyrosines. In addition to hyperactivity in sugar consumption, the absence of TmaR also leads to detrimental effects on the ability of cells to survive in mild acidic conditions. Our results argue that this survival defect, which is sugar- and EI-dependent, reflects the difficulty of cells lacking TmaR to enter stationary phase. Our study identifies TmaR as the first E. coli protein reported to localize in a tyrosine-dependent manner and to control the activity of other proteins by their polar sequestration and release. SIGNIFICANCEIn recent years, we have learnt that bacterial cells have intricate spatial organization despite the lack of membrane-bounded organelles. The endcaps of rod-shaped bacteria, termed poles, are emerging as hubs for sensing and responding, but the underlying mechanisms for positioning macromolecules there are largely unknown. We discovered a novel protein, TmaR, whose polar localization depends on a phospho-tyrosine modification. We show that TmaR controls the activity of EI, the major regulator of sugar metabolism in most bacteria, by polar sequestration and release. Notably, TmaR is essential for survival in conditions that E. coli often encounters in nature. Hence, TmaR is a key regulator that connects tyrosine phosphorylation, spatial regulation, sugar metabolism and survival in bacteria and the first protein reported to recruit proteins to the E. coli cell poles.

microbiology↗