The essential peptidoglycan glycosyltransferase MurG forms a complex with proteins involved in lateral envelope growth as well as with proteins involved in cell division in Escherichia coli

In Escherichia coli many enzymes including MurG are directly involved in the synthesis and assembly of peptidoglycan. MurG is an essential glycosyltransferase catalysing the last intracellular step of peptidoglycan synthesis. To elucidate its role during elongation and division events, localization of MurG using immunofluorescence microscopy was performed. MurG exhibited a random distribution in the cell envelope with a relatively higher intensity at the division site. This mid-cell localization was dependent on the presence of a mature divisome. Its localization in the lateral cell wall appeared to require the presence of MreCD. This could be indicative of a potential interaction between MurG and other proteins. Investigating this by immunoprecipitation revealed the association of MurG with MreB and MraY in the same protein complex. In view of this, the loss of rod shape of ΔmreBCD strain could be ascribed to the loss of MurG membrane localization. Consequently, this could prevent the localized supply of the lipid II precursor to the peptidoglycan synthesizing machinery involved in cell elongation. It is postulated that the involvement of MurG in the peptidoglycan synthesis concurs with two complexes, one implicated in cell elongation and the other in division. A model representing the first complex is proposed

Inteferon-gamma induces gp91phox expression in human monocytes via protein kinase C-dependent phosphorylation of PU.1.

We previously reported that the stimulation of human blood monocytes with IFN-gamma induces the binding of PU.1 to the gp91phoxpromoter and the consequent expression of gp91phox. In this study,we show that the effect of IFN-gamma is reproduced by the serine phosphatase inhibitor,okadaic acid,and this suggests that serine kinases could be involved in gp91phox expression. We also show that IFN-gamma induces the serine/threonine phosphorylation of PU.1 in cultured monocytes. This phosphorylation,as well as the IFN-gamma-induced PU.1 binding and gp91phox protein synthesis,is slightly affected by the casein kinase II inhibitor,daidzein,but is abrogated by the protein kinase C (PKC) inhibitor Go6976,and by synthetic peptides with sequences based on the endogenous pseudosubstrate region of the classical PKC alpha and beta isoforms. In contrast,peptides reproducing the pseudosubstrate region of PKC epsilon were without effect. Moreover,we found that the treatment of monocytes with IFN-gamma induces the nuclear translocation and the activation of PKC alpha and beta I,but not of PKC beta II,and that the IFN-gamma-induced phosphorylation of PU.1 was greatly reduced by LY333531,a selective inhibitor of PKC beta isoforms. Finally,nuclear run-on assays demonstrated that while the PKC inhibitors,Go6976 and LY333531,decrease the IFN-gamma induced gp91phox transcription,the serine phosphatase inhibitor,enhances the gp91phox gene transcription. Our results indicate that in cultured monocytes,IFN-gamma induces the binding of PU.1 to the gp91phox promoter and the expression of gp91phox by phosphorylation of PU.1 via activation of PKC alpha and/or beta