1. Mechanisms underlying CCR and inducer exclusion in enteric bacteria.
Mechanisms underlying CCR and inducer exclusion in enteric bacteria. The import of glucose and other PTS carbohydrates leads to net dephosphorylation of the PTS proteins (including EIIAGlc and the B domain of EIIBCGlc) and thereby to inducer exclusion and recruitment of the transcription regulator Mlc to the membrane. The upper left part of the figure shows that unphosphorylated EIIAGlc blocks the import of lactose, maltose, and melibiose and the phosphorylation of glycerol by binding to the respective transporter or kinase. The upper right part of the figure shows recruitment of Mlc by unphosphorylated EIIBCGlc, which prevents the regulator from binding to its target sites on the DNA. In the absence of glucose and in the presence of phosphoenolpyruvate, the PTS proteins are found mainly in the phosphorylated state. The central part of the figure shows that phosphorylated EIIAGlc activates adenylate cyclase (AC) but probably only in the presence of an unknown adenylate cyclase activation factor (ACAF). Adenylate cyclase binds phosphorylated as well as unphosphorylated EIIAGlc (see reference 632). The bottom part of the figure shows the effect of the activated transcription factors (free Mlc and Crp:cAMP) on the transcription of the genes encoding Crp, adenylate cyclase, Mlc, and EIIBCGlc, respectively. The inset shows the Crp:cAMP concentration dependence of crp transcription (deduced from data reported in references 310 and 311). The arrow indicates the physiological concentration of activated Crp in exponentially growing cells in the absence of PTS carbohydrates.
Josef Deutscher et al. Microbiol. Mol. Biol. Rev. 2006; doi: /MMBR