Highlights d Lack of reactive oxygen species, or reductive stress, prevents myogenesis d Reductive stress reverses oxidation of invariant Cys residues in FNIP1 d Only reduced, but not oxidized, FNIP1 is polyubiquitylated by CUL2 FEM1B d FNIP1 degradation leads to activation of mitochondria to recalibrate ROS

The bacterial phosphoenolpyruvate:sugar phosphotransferase system (PTS) is a multicomponent system that participates in a variety of physiological processes in addition to the phosphorylation-coupled transport of numerous sugars. In Escherichia coli and other enteric bacteria, enzyme IIA Glc (EIIA Glc ) is known as the central processing unit of carbon metabolism and plays multiple roles, including regulation of adenylyl cyclase, the fermentation/respiration switch protein FrsA, glycerol kinase, and several non-PTS transporters, whereas the only known regulatory role of the E. coli histidine-containing phosphocarrier protein HPr is in the activation of glycogen phosphorylase. Because HPr is known to be more abundant than EIIA Glc in enteric bacteria, we assumed that there might be more regulatory mechanisms connected with HPr. The ligand fishing experiment in this study identified Rsd, an anti-sigma factor known to complex with σ 70 in stationary-phase cells, as an HPr-binding protein in E. coli. Only the dephosphorylated form of HPr formed a tight complex with Rsd and thereby inhibited complex formation between Rsd and σ 70. Dephosphorylated HPr, but not phosphorylated HPr, antagonized the inhibitory effect of Rsd on σ 70-dependent transcriptions both in vivo and in vitro, and also influenced the competition between σ 70 and σ S for core RNA polymerase in the presence of Rsd. Based on these data, we propose that the anti-σ 70 activity of Rsd is regulated by the phosphorylation state-dependent interaction of HPr with Rsd.glucose signaling | sigma factor competition | transcriptional regulation B y monitoring their environment, bacteria ensure the most appropriate response for each environment. One of the sensory systems for monitoring changes in nutrient availability is the phosphoenolpyruvate (PEP):sugar phosphotransferase system (PTS). The PTS is a multicomponent system that catalyzes the concomitant phosphorylation and translocation of numerous sugar substrates across the cytoplasmic membrane. This system consists of two general components, enzyme I (EI) and the histidine-containing phosphocarrier protein HPr, which are common to all PTS sugars, along with many sugar-specific components collectively known as enzyme IIs (EIIs) (1, 2).Each EII complex generally consists of three domains: one integral membrane domain forming the sugar translocation channel (EIIC) and two cytosolic domains (EIIA and EIIB). EI transfers a phosphoryl group from PEP to HPr, and HPr then transfers the phosphoryl group to the different EIIs. Each EII complex forms a cascade of phosphorylated intermediates, and in the presence of a PTS sugar, the EIIA and EIIB domains sequentially transfer the phosphate group from HPr to the incoming sugar. Thus, the phosphorylation states of the PTS components change depending on the availability of a PTS sugar substrate (3, 4).In addition to sugar uptake, the PTS plays an important role as a sensory transduction system to monitor nutritional changes, and its components are involved in the regula...

Preferential sugar utilization is a widespread phenomenon in biological systems. Glucose is usually the most preferred carbon source in various organisms, especially in bacteria where it is taken up via the phosphoenolpyruvate:sugar phosphotransferase system (PTS). The currently proposed model for glucose preference over non-PTS sugars in enteric bacteria including E. coli is strictly dependent on the phosphorylation state of the glucose-specific PTS component, enzyme IIAGlc (EIIAGlc). However, the mechanism of the preference among PTS sugars is largely unknown in Gram-negative bacteria. Here, we show that glucose preference over another PTS sugar, mannitol, is absolutely dependent on the general PTS component HPr, but not on EIIAGlc, in E. coli. Dephosphorylated HPr accumulates during the transport of glucose and interacts with the mannitol operon regulator, MtlR, to augment its repressor activity. This interaction blocks the inductive effect of mannitol on the mannitol operon expression and results in the inhibition of mannitol utilization.

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Carbon catabolite repression is a regulatory mechanism to ensure sequential utilization of carbohydrates and is usually accomplished by repression of genes for the transport and metabolism of less preferred carbon compounds by a more preferred one. Although glucose and mannitol share the general components, enzyme I and HPr, of the phosphoenolpyruvate-dependent phosphotransferase system (PTS) for their transport, glucose represses the transport and metabolism of mannitol in a manner dependent on the mannitol operon repressor MtlR in Escherichia coli. In a recent study, we identified the dephosphorylated form of HPr as a regulator determining the glucose preference over mannitol by interacting with and augmenting the repressor activity of MtlR in E. coli. Here, we determined the X-ray structure of the MtlR-HPr complex at 3.5 Å resolution to understand how phosphorylation of HPr impedes its interaction with MtlR. The phosphorylation site (His15) of HPr is located close to Glu108 and Glu140 of MtlR and phosphorylation at His15 causes electrostatic repulsion between the two proteins. Based on this structural insight and comparative sequence analyses, we suggest that the determination of the glucose preference over mannitol solely by the MtlR-HPr interaction is conserved within  the Enterobacteriaceae family.