Relationship between pseudo-HPr and the PEP: fructose phosphotransferase system in Salmonella typhimurium and Escherichia coli

Abstract

We have studied in Salmonella typhimurium and Escherichia coli the properties of pseudo-HPr suppressor mutations. These mutations suppressed the defects in a ptsH mutant which lacks HPr, one of the enzymes of the phosphoenolpyruvate: carbohydrate phosphotransferase system. The suppressor mutation was mapped in S. typhimurium at 3 min, closely linked to leu. The corresponding chromosomal fragment of 1.7 kb from S. typhimurium and E. coli (extending clockwise from ilvH) was cloned. In a maxicell system a protein with an approximate molecular weight of 36,000 was synthesized. Pseudo-HPr suppressor mutations (fruR) and a deletion extending clockwise from leu resulted in the constitutive expression of the fru operon containing the genes for IIFru (fruA), IIIFru (fruB), fructose 1-phosphate kinase (fruK) and pseudo-HPr (fruF). fruR probably codes for a repressor of the fru operon. Tn10 mutagenesis revealed the following order of genes in the fru operon: fruB-(fruK, fruF)-fruA. Pseudo-HPr activity could replace HPr in PEP-dependent phosphorylation of PTS carbohydrates. IIIFru could be phosphorylated both via HPr and pseudo-HPr, since mutants lacking pseudo-HPr activity were still able to phosphorylate fructose in the presence of added HPr. Both the pseudo-HPr suppressor mutations at 3 min and the deletion extending from leu had an additional phenotype. Introduction of these mutations or deletions was always accompanied by disappearance of PEP synthase activity. Complementation of such a mutant with the cloned fragments reversed both phenotypes at the same time. Possibly, the fruR gene product acts as an activator of the gene coding for PEP synthase.

How Phosphotransferase System-Related Protein Phosphorylation Regulates Carbohydrate Metabolism in Bacteria

“…The large-scale transcriptional responses in E. coli are mediated via a limited number of global regulators (527). In enteric bacteria, global regulation of carbon metabolism involves several and transcription factors such as Crp (cyclic AMP receptor protein) (reviewed in references 76,95,96,416, and 636), Mlc (666), FruR (145,267,268,762), CsrA (carbon storage regulator) (451,742,743,752,861), and 54 (25,150,843). The activities of some of these regulators are directly affected by the PTS.…”

Molecular characterization of glucokinase from Escherichia coli K-12

“…Only a mutation in fruR (33,34) abolishing the function of this global regulator (36) had a small stimulating effect on the expression of glk. This is consistent with the twofold reduction in glk expression with glucose as the carbon source.…”

Regulatory interactions involving the proteins of the phosphotransferase system in enteric bacteria

“…Evidence has been presented suggesting that the fructose repressor, FruR, and possibly other His83 (equivalent to His 90 in the E coh protein) is located at the C-terminus of the central p-strand B: Computer-generated space-filling model of the llAglC molecule The orientation is the same as in A Two perpendicular histidyl side chains can be seen at the top third of the molecule The histidine on the right is the active-site His83, and to the left io His68 (reproduced from Liao et al , 1991, with permission) proteins encoded within the fructose ( f r u ) regulon of Salmonella typhimurium play a key role in the transcriptional regulation of central pathways of carbon source degradation and carbohydrate synthesis [Geerse et al, 1986[Geerse et al, , 1989aChin et al, 1987,19891. These pathways include the anaerobic glycolytic pathway (negatively controlled by FruR) and aerobic pathways of gluconeogenesis, the glyoxalate shunt, and the Krebs cycle (positively controlled by FruR) [Chin et al, 19891.…”