Bacterial phosphotransferase system: regulation of the glucose and mannose enzymes II by sulfhydryl oxidation

Involvement of the mannose phosphotransferase system of Lactobacillus plantarum WCFS1 in peroxide stress tolerance

A Lactobacillus plantarum strain with a deletion in the gene rpoN, encoding the alternative sigma factor 54 (sigma(54)), displayed a 100-fold-higher sensitivity to peroxide than its parental strain. This feature could be due to sigma(54)-dependent regulation of genes involved in the peroxide stress response. However, transcriptome analyses of the wild type and the mutant strain during peroxide exposure did not support such a role for sigma(54). Subsequent experiments revealed that the impaired expression of the mannose phosphotransferase system (PTS) operon in the rpoN mutant caused the observed increased peroxide sensitivity.

sigma54-Mediated control of the mannose phosphotransferase sytem in Lactobacillus plantarum impacts on carbohydrate metabolism

Sigma factors direct specific binding of the bacterial RNA polymerase to the promoter. Here we present the elucidation of the sigma(54 ) regulon in Lactobacillus plantarum. A sequence-based regulon prediction of sigma(54)-dependent promoters revealed an operon encoding a mannose phosphotransferase system (PTS) as the best candidate for sigma(54)-mediated control. A sigma (54) (rpoN) mutant derivative did not grow on mannose, confirming this prediction. Additional mutational analyses established the presence of one functional mannose PTS in L. plantarum, the expression of which is controlled by sigma(54) in concert with the sigma(54)-activator ManR. Genome-wide transcription comparison of the wild-type and the rpoN-deletion strain revealed nine upregulated genes in the wild-type, including the genes of the mannose PTS, and 21 upregulated genes in the rpoN mutant. The sigma(54)-controlled mannose PTS was shown also to transport glucose in L. plantarum wild-type cells, and its presence causes a lag phase when cultures are transferred from glucose- to galactose-containing media. The mannose PTS appeared to drain phosphoenolpyruvate (PEP) pools in resting cells, since no PEP could be detected in resting wild-type cells, while mannose PTS mutant derivatives contained 1-3 muM PEP (mg protein)(-1 ). Our data provide new insight into the role of sigma( 54) in L. plantarum and possibly other Gram-positive bacteria in the control of expression of an important glucose transporter that contributes to glucose-mediated catabolite control via modulation of the PEP pool.

Molecular analysis of the phosphoenolpyruvate-dependent L-sorbose: phosphotransferase system from Klebsiella pneumoniae and of its multidomain structure

We have cloned a 3.4 kb DNA fragment from the chromosome of Klebsiella pneumoniae that codes for a phosphoenolpyruvate-dependent L-sorbose: phosphotransferase system (PTS). The cloned fragment was sequenced and four open reading frames coding for 135 (sorF), 164 (sorB), 266 (sorA) and 274 (sorM) amino acids, respectively, were found. The corresponding proteins could be detected in a T7 overexpression system, which yielded molecular masses of about 14,000 for SorF, 19,000 for SorB, 25,000 for SorA and 27,000 for SorM. SorF and SorB have all the characteristics of soluble and intracellular proteins in accordance with their functions as EIIASor and EIIBSor domains of the L-sorbose PTS. SorA and SorM, by contrast, are strongly hydrophobic, membrane-bound proteins with two to five putative transmembrane helices that alternate with a series of hydrophilic loops. They correspond to domains EIICSor and EIIDSor. The four proteins of the L-sorbose PTS resemble closely (27%-60%) the four subunits of a D-fructose PTS (EIIALev, EIIBLev, EIICLev, and EIIDLev) from Bacillus subtilis and the three subunits of the D-mannose PTS (EIIA,BMan, EIICMan, and EIIDMan) from Escherichia coli K-12. The three systems constitute a new PTS family, and sequence comparisons revealed highly conserved structures for the membrane-bound proteins. A consensus sequence for the membrane proteins was used to postulate a model for their integration into the membrane.

Phosphoenolpyruvate:carbohydrate phosphotransferase systems of bacteria

Numerous gram-negative and gram-positive bacteria take up carbohydrates through the phosphoenolpyruvate (PEP):carbohydrate phosphotransferase system (PTS). This system transports and phosphorylates carbohydrates at the expense of PEP and is the subject of this review. The PTS consists of two general proteins, enzyme I and HPr, and a number of carbohydrate-specific enzymes, the enzymes II. PTS proteins are phosphoproteins in which the phospho group is attached to either a histidine residue or, in a number of cases, a cysteine residue. After phosphorylation of enzyme I by PEP, the phospho group is transferred to HPr. The enzymes II are required for the transport of the carbohydrates across the membrane and the transfer of the phospho group from phospho-HPr to the carbohydrates. Biochemical, structural, and molecular genetic studies have shown that the various enzymes II have the same basic structure. Each enzyme II consists of domains for specific functions, e.g., binding of the carbohydrate or phosphorylation. Each enzyme II complex can consist of one to four different polypeptides. The enzymes II can be placed into at least four classes on the basis of sequence similarity. The genetics of the PTS is complex, and the expression of PTS proteins is intricately regulated because of the central roles of these proteins in nutrient acquisition. In addition to classical induction-repression mechanisms involving repressor and activator proteins, other types of regulation, such as antitermination, have been observed in some PTSs. Apart from their role in carbohydrate transport, PTS proteins are involved in chemotaxis toward PTS carbohydrates. Furthermore, the IIAGlc protein, part of the glucose-specific PTS, is a central regulatory protein which in its nonphosphorylated form can bind to and inhibit several non-PTS uptake systems and thus prevent entry of inducers. In its phosphorylated form, P-IIAGlc is involved in the activation of adenylate cyclase and thus in the regulation of gene expression. By sensing the presence of PTS carbohydrates in the medium and adjusting the phosphorylation state of IIAGlc, cells can adapt quickly to changing conditions in the environment. In gram-positive bacteria, it has been demonstrated that HPr can be phosphorylated by ATP on a serine residue and this modification may perform a regulatory function.

Oxidative stress responses in Escherichia coli and Salmonella typhimurium

Oxidative stress is strongly implicated in a number of diseases, such as rheumatoid arthritis, inflammatory bowel disorders, and atherosclerosis, and its emerging as one of the most important causative agents of mutagenesis, tumorigenesis, and aging. Recent progress on the genetics and molecular biology of the cellular responses to oxidative stress, primarily in Escherichia coli and Salmonella typhimurium, is summarized. Bacteria respond to oxidative stress by invoking two distinct stress responses, the peroxide stimulon and the superoxide stimulon, depending on whether the stress is mediated by peroxides or the superoxide anion. The two stimulons each contain a set of more than 30 genes. The expression of a subset of genes in each stimulon is under the control of a positive regulatory element; these genes constitute the OxyR and SoxRS regulons. The schemes of regulation of the two regulons by their respective regulators are reviewed in detail, and the overlaps of these regulons with other stress responses such as the heat shock and SOS responses are discussed. The products of Oxy-R- and SoxRS-regulated genes, such as catalases and superoxide dismutases, are involved in the prevention of oxidative damage, whereas others, such as endonuclease IV, play a role in the repair of oxidative damage. The potential roles of these and other gene products in the defense against oxidative damage in DNA, proteins, and membranes are discussed in detail. A brief discussion of the similarities and differences between oxidative stress responses in bacteria and eukaryotic organisms concludes this review.

Catfish liver acid phosphatases: differently glycosylated enzyme molecules with altered kinetic properties

Two forms of catfish liver acid phosphatase (AcPase I and II) were separated and purified to homogeneity and their carbohydrate compositions and some biochemical properties were studied. Evidence is given that AcPase I and II are differently glycosylated forms of the same enzyme. The enzyme forms differ significantly in the size and the composition of their carbohydrate components, sensitivity towards sulfhydryl-blocking and protecting reagents, sensitivity to ferric and ferrous ions, thermostability and ability to hydrolyze some nucleotides. The more highly glycosylated form is more sensitive to thermal denaturation. AcPase I and II behave differently towards ascorbate and changes in its concentration and it is suggested that the concentration of reducing modifiers may regulate AcPase activity at the cellular level. It is hypothesized that the differing extents of glycosylation influence the structure of the enzyme forms. This is expressed in altered conformations of two enzyme forms and results in a different exposure of the essential cysteine residues.