Phosphotransferase receptors

The chemotaxis receptors for PTS carbohydrates are enzymes II [10]— membrane proteins that transport certain hexoses, hexosamines, polyhy-dric alcohols, and disaccharides [582, 602]. The mechanism of transport involves activation of enzyme II by phosphorylation, carried out by two cytoplasmic protein kinases enzyme I and histidine-containing protein (HPr) [582], Unlike the case of the periplasmic binding proteins, the PTS primary receptor—enzyme II—does not interact directly with an MCP As will be discussed in Section 8.2.7, it is enzyme I which links the occupancy of enzyme II with the chemotaxis system. 

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Man 6-P receptors, located in the Golgi apparatus, bind the Man 6-P residue of these enzymes and direct them to the lysosomes. Fibroblasts from patients with I-cell disease (see below) are severely deficient in the activity of the GIcNAc phosphotransferase. 

Eukaryotic ABC transport system Phosphotransferase system (PTS) Ion-coupled transport system Signal Transduction Two-component system Bacterial chemotaxis MAPK signaling pathway Second messenger signaling pathway Ligand-Receptor Interaction G-protein-coupled receptors Ion-channel-linked receptors Cytokine receptors Molecular Assembly Ribosome assembly Flagellar assembly Enzyme assembly... 

The protein kinase family encompasses more than three hundred members of critically important enzymes, each one with a specific role or function within the cell. These enzymes, ATP-phosphotransferases, recognize target proteins and through the phosphorylation of specific sites either activate or deactivate a particular pathway of signal transduction. Many of these signaling pathways are associated with cell surface receptors, which are located in the membranes that surround cells. The difference between the families of protein kinases is that they have different targets and generally fall into two major classes ... 

It is postulated that inhibition of PtdCho synthesis and the release of choline are key steps associated with excitotoxicity and are common to NMDA and AMPA receptor stimulation. The mechanism of inhibition of PtdCho is not fully understood. Metabolic labeling experiments in cortical cultures demonstrate that NMDA receptor over activation does not modify the activity of phosphochohne or phospho-ethanolamine cytidylyltransferases but strongly inhibits choline and ethanolamine phosphotransferase activities. This effect is observed well before any significant membrane damage and cell death. Moreover, cholinephosphotransferase activity is lower in microsomes from NMDA-treated cells. These results show that membrane... 

Gasull T., Sarri E., DeGregorio-Rocasolano N., and Trullas R. (2003). NMDA receptor overactivation inhibits phospholipid synthesis by decreasing choline-ethanolamine phosphotransferase activity. J. Neurosci. 23 4100 1107. 

Resistance can be caused by 1) decreased uptake of drug when the oxygen-dependent transport system for aminoglycosides is absent an altered receptor where the 30S ribosomal subunit binding site has a lowered affinity for aminoglycosides plasmid-associated synthesis of enzymes (for example, acetyltransferases, nucleotidyltransferases, and phosphotransferases) that modify and inactivate aminoglycoside... 

Abbreviations ERK, extracellular signal-regulated kinase GPCR, G-protein-coupled receptor MCP, methyl-accepting chemotaxis protein PIP3, phophatidylinositol triphosphate PLCy, phospholipase Cy PTS, phosphoeno/pyruvate-dependent carbohydrate phosphotransferase system. At least in the sea urchin. 

Figure 9.2 Glucose transport system and carbon catabolite repression reiated with giucose-specific phosphotransferase system in Escherichia coli. MgIBAC the gaiactose ABC transporter GaiP the galactose H+ symporter CRP the cAMP receptor protein PEP phosphoenoipyruvate.

The chemotactic receptors to glucose, fructose, mannose and certain other sugars are insensitive to osmotic shock (Table 4.1) and have been shown to be integral parts of the cytoplasmic membrane. These membrane-associated receptors have been shown to be identical with enzymes II, the substrate-specific components of phosphotransferase transport (the PEP system). The essential event during sugar translocation using the PEP system is the phosphoenolpyruvate-dependent phosphorylation of the... 

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