Spatial and temporal organization of the E. coli PTS components

Abstract

The phosphotransferase system (PTS) controls preferential use of sugars in bacteria. It comprises of two general proteins, enzyme I (EI) and HPr, and various sugar-specific permeases. Using fluorescence microscopy, we show here that EI and HPr localize near the Escherichia coli cell poles. Polar localization of each protein occurs independently, but HPr is released from the poles in an EI- and sugar-dependent manner. Conversely, the β-glucoside-specific permease, BglF, localizes to the cell membrane. EI, HPr and BglF control the β-glucoside utilization (bgl) operon by modulating the activity of the BglG transcription factor; BglF inactivates BglG by membrane sequestration and phosphorylation, whereas EI and HPr activate it by an unknown mechanism in response to β-glucosides availability. Using biochemical, genetic and imaging methodologies, we show that EI and HPr interact with BglG and affect its subcellular localization in a phosphorylation-independent manner. Upon sugar stimulation, BglG migrates from the cell periphery to the cytoplasm through the poles. Hence, the PTS components appear to control bgl operon expression by ushering BglG between the cellular compartments. Our results reinforce the notion that signal transduction in bacteria involves dynamic localization of proteins.

The compartmentalized vessel

“…Notably, when bglG is transcribed without bglF, its transcripts localize to the poles, 25 where the BglG protein forms a complex with the general PTS proteins after it is released from the membrane pre-complex upon sugar stimulation. 12 To the best of my knowledge, this is the first demonstration of changes in mRNA localization depending on changes in the site of complex formation in response to environmental stimuli in any organism. Summarily, our study establishes for the first time the existence of translationindependent mechanisms for targeting bacterial mRNAs to the subcellular regions where their protein products are subsequently detected.…”

“…11 Why has the cell evolved a polarly localized complex to control organelles that are scattered around the cell periphery? In a study that we recently published in the EMBO Journal, 12 we showed that the control center of the PTS system, which consists of the general PTS proteins, EI and HPr, also localizes to the cell poles. The different proteins that are regulated by this polar center via HPrmediated phosphorylation localize around the cell circumference (sugar permeases) or in the cytoplasm (e.g., IIA glc ).…”

“…The small HPr protein is released from the poles upon sugar stimulation to execute its tasks in the different cellular sub-domains. 12 Hence the PTS and the chemotaxis systems utilize a similar strategy; that is, their command centers cluster near the poles, whereas small proteins, which act as messengers, shuttle between the poles and other cellular domains, where they execute their roles. It seems reasonable that localization of the two systems near the poles should facilitate communication between their components and improve the coordination of their actions.…”

“…We showed that localization of the BglG transcription factor, which enables expression of a PTS sugar utilization operon, bgl, is determined by its consecutive interaction with different PTS components, i.e., with the PTS sugar permease BglF, which localizes around the cell circumference, and with the general PTS proteins at the poles. 12,17 Hence, upon sugar stimulation, BglG migrates from the cell periphery to the cytoplasm through the poles (Fig. 1).…”

“…18 Indeed, we have now shown that the interaction of BglG with the different PTS components, which determines its subcellular localization, does not depend on the phosphorylation state of the different players. 12 Hence, the PTS components control bgl operon expression by ushering the BglG transcription factor between the different cellular compartments in response to environmental signals. These results clearly indicate that signal transduction in bacteria involves dynamic localization of proteins.…”