Group Translocation – PEP : PTS

Abstract

The phosphoenolpyruvate:carbohydrate phospho‐transferase system (PEP:PTS) is a prokaryotic enzyme/transport system that phosphorylates its extracellular carbohydrate substrates during transport, leading to intracellular accumulation of the sugar phosphate esters. Several phosphoryl transfer proteins play essential roles in sugar uptake, and they comprise a phosphoryl transfer chain using PEP as the phosphoryl donor, and the incoming sugar as the ultimate phosphoryl acceptor. This phosphoryl transfer chain is: PEP→EI→HPr→IIA→IIB+ IIC→sugar, where E=Enzyme and HPr=a small heat stable, histidine‐containing protein, and only the IIC constituent, the transport protein, is not phosphorylated. In mixtures of carbon sources, preferential growth on PTS substrates often occurs, as the phosphorylation state of PTS proteins coordinates the activities and synthesis of enzymes that initiate sugar metabolism. The mechanisms of regulation are different in representative Gram‐negative and Gram‐positive bacteria, but in both cases the PTS plays a central role. The PTS in Escherichia coli accomplishes this goal by regulating both cyclic adenosine monophosphate (AMP) synthesis and the uptake of sugar inducers of enzyme synthesis. It also plays a role in the coordination of nitrogen metabolism with carbon metabolism. In many bacteria, the PTS serves as a chemosensory system, directing movement of bacteria up concentration gradients of PTS sugars. In a few bacteria, the PTS functions in regulation but not in sugar uptake. Although this enzyme system has not been found in eukaryotes, it has been identified in archaea. The PTS is thus a multifunctional enzyme/transport/sensor/regulatory system that coordinates many activities in prokaryotic cells. Key Concepts: Biological membranes provide the fundamental barrier that separates the inside of a cell (the cytoplasm) from the extracellular space. Embedded in these structures are proteins, many of which transport substances across the membrane. The phosphotransferase system (PTS) serves as a complex transport system. It consists of energy‐coupling enzymes (Enzymes I, HPr, IIA and IIB) as well as the PTS permeases (Enzymes IIC or IICs). The IIC components couple phosphoryl transfer from IIB∼P to sugar substrate phosphorylation. The process of coupled sugar uptake with sugar phosphorylation, involving substrate modification, is called ‘group translocation’. The PTS serves as a chemoreception system, directing the activity of the bacterial flagellum so that bacteria swim up concentration gradients of nutrient sugars. The PTS is a complex multifaceted system, regulating the activities of many non‐PTS enzymes and transporters, thereby creating a hierarchical system of carbon sources. PTS protein domains are incorporated into many transcription factors, enzymes and transporters, allowing it to regulate these determinants of prokaryotic cell physiology and pathology. A comprehensive understanding of prokaryotic cell biology requires a detailed understanding of the PTS.