Abstract
Besides the canonical phosphoenolpyruvate-dependent phosphotransferase system (PTS) for carbohydrate transport, most Proteobacteria possess the so-called nitrogen PTS (PTSNtr) that transfers a phosphate group from phosphoenolpyruvate (PEP) over enzyme INtr (EINtr) and NPr to enzyme IIANtr (EIIANtr). The PTSNtr lacks membrane-bound components and functions exclusively in a regulatory capacity. While EIIANtr has been implicated in a variety of cellular processes such as potassium homeostasis, phosphate starvation, nitrogen metabolism, carbon metabolism, regulation of ABC transporters and poly-β-hydroxybutyrate accumulation in many Proteobacteria, the only identified role of NPr is the regulation of biosynthesis of the lipopolysaccharide (LPS) layer by direct interaction with LpxD in Escherichia coli. In this study, we provide another phenotype related to NPr. Several lines of evidence demonstrate that E. coli strains with increased levels of dephosphorylated NPr are sensitive to envelope stresses, such as osmotic, ethanol and SDS stresses, and these phenotypes are independent of LpxD. The C-terminal region of NPr plays an important role in sensitivity to envelope stresses. Thus, our data suggest that the dephospho-form of NPr affects adaptation to envelope stresses through a C-terminus-dependent mechanism.
Highlights
The bacterial phosphoenolpyruvate : sugar phosphotransferase system is a group translocation system that mediates the translocation and concomitant phosphorylation of many sugars across the cytoplasmic membrane (Deutscher et al, 2006)
The nitrogen phosphotransferase system (PTS) constitutes another phosphoryl-transfer cascade whose relay proceeds sequentially from phosphoenolpyruvate (PEP) to enzyme INtr (EINtr) encoded by ptsP, NPr encoded by ptsO and enzyme IIANtr (EIIANtr) encoded by ptsN, which are homologous to the sugar PTS components enzyme I (EI), histidine phosphocarrier protein (HPr) and EIIA, respectively (Peterkofsky et al, 2006; Pfluger-Grau & Gorke, 2010; Powell et al, 1995)
Mutant strains deleted for the nitrogen PTS genes did not show any significant difference in growth compared to WT when grown in LB medium or under acid stress conditions (Fig. 1)
Summary
The bacterial phosphoenolpyruvate : sugar phosphotransferase system (sugar PTS) is a group translocation system that mediates the translocation and concomitant phosphorylation of many sugars across the cytoplasmic membrane (Deutscher et al, 2006) This system consists of two cytoplasmic general proteins, enzyme I (EI) and histidine phosphocarrier protein (HPr), which lack sugar specificity, and sugar-specific enzyme II (EII) components which usually have three domains, two cytosolic domains (EIIA and EIIB) and one membranous domain (EIIC) (Postma et al, 1993). In addition to sugar uptake and phosphorylation, the sugar PTS plays important roles in the regulation of numerous metabolic processes by sensing the availability of nutrients These regulatory functions include activation of adenylyl cyclase (Park et al, 2006), Abbreviations: EI, enzyme I; EII, enzyme II; HPr, histidine phosphocarrier protein; LPS, lipopolysaccharide; PEP, phosphoenolpyruvate; PTS, PEP : carbohydrate phosphotransferase system.
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