Phosphotransferase system

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The active transport process by group translocation through a cell membrane, above for Escherichia coli , below for Bacillus subtilis using the example of glucose.

The phosphotransferase system ( PTS ), more precisely phosphoenolpyruvate phosphotransferase system ( PEP-PTS ) is an active material transport system of microorganisms that works via group translocation . So far it has only been found in bacteria .

Here, the high-energy phosphate residue of phosphoenolpyruvate (PEP) is transferred via several protein kinases ( signal transduction ) first to the "intermediary proteins " and finally to the substrate, usually hexoses ( glucose , mannose , fructose ) or sugar alcohols (e.g. glucitol , mannitol ). The substrate is introduced into the cytoplasm by membrane proteins (translocases that act independently of energy and therefore only establish an equilibrium) , where it is finally phosphorylated . This removes the equilibrium from the substrate molecule because the transporter can only bind and translocate unphosphorylated molecules. For this reason, the cell can pump the substrates into the cell against the concentration gradient. PEP provides the energy for this, converting it to pyruvate .

procedure

The first reaction step consists of the transfer of the phosphate residue from PEP to the unspecific enzyme I (EI) by self-phosphorylation, which then phosphorylates a histidine- containing protein (HPr) on its histidine residue. EI and HPr are either constitutively expressed or partially inducible and are located at the cell poles. Only the following transfer steps to the enzyme complex enzyme II (EII) are substrate-specific . This is made up of at least three domains (A to C) which, depending on the system, fuse to form a complex or can be present separately in the cytoplasm of the cell. The actual transport protein here is the enzyme II C, which is integrated into the membrane. Enzyme IIB is the only component of this system that is phosphorylated on a cysteine ​​residue ; all other components are transferred to a histidine residue. EII are located on the cell periphery and are expressed through the presence of the corresponding sugar. To differentiate between the substrate, the corresponding three-letter abbreviations are used as a superscript; this is how the glucose-specific EIIA component is called EIIA Glc , whereas a mannitol-specific EIIC component is called EIIC Mtl .

The PTS is also involved in the regulation of the metabolic pathways. Since many chemoheterotrophic bacteria use glucose as their preferred carbon source, metabolic pathways for utilizing other sugars are switched off at the transcription level when it becomes available ( catabolite repression ). The E IIA protein for glucose transport from Escherichia coli , in its phosphorylated form, activates adenylate cyclase , which cAMP synthesizes. With its receptor protein CRP, cAMP acts as a transcription activator for the expression of genes whose products enable the uptake of alternative carbon sources.

In its dephosphorylated form, E IIA also inhibits transporters for the uptake of other sugars.

Substrates

The PEP-PTS accepts keto- and aldohexoses, di- and trisaccharides , sugar alcohols , amino sugars , gluconic acids , glucose aminate, glucoselysine and fructoselysine. These substrates are also known as PTS sugars.

In contrast, non-PTS sugars are brought into the cell by permeases or ABC transporters , such as. B. glycerin , glucuronate or D - arabinose .

literature

  • Anne Galinier, Josef Deutscher: Sophisticated Regulation of Transcriptional Factors by the Bacterial Phosphoenolpyruvate: Sugar Phosphotransferase System . In: Journal of Molecular Biology . tape 429 , no. 6 , March 24, 2017, p. 773–789 , doi : 10.1016 / j.jmb.2017.02.006 .
  • Milton H. Saier: The Bacterial Phosphotransferase System: New Frontiers 50 Years after Its Discovery . In: Journal of Molecular Microbiology and Biotechnology . tape 25 , no. 2-3 , 2015, p. 73-78 , doi : 10.1159 / 000381215 , PMID 26159069 , PMC 4512285 (free full text).
  • J. Deutscher, C. Francke, PW Postma: How phosphotransferase system-related protein phosphorylation regulates carbohydrate metabolism in bacteria. In: Microbiol Mol Biol Rev. Volume 70, No. 4, 2006, pp. 939-1031. PMID 17158705 ; PDF (free full text access)

Individual evidence

  1. ↑ 4.A: Phosphotransfer-driven group translocators. In: TCDB. Saier Lab Bioinformatics, accessed on September 16, 2010 .
  2. ^ A b c Anne Galinier, Josef Deutscher: Sophisticated Regulation of Transcriptional Factors by the Bacterial Phosphoenolpyruvate: Sugar Phosphotransferase System . In: Journal of Molecular Biology . tape 429 , no. 6 , March 24, 2017, p. 773–789 , doi : 10.1016 / j.jmb.2017.02.006 .