The regulation of the ptsG gene encoding the glucose transporter JAK inhibitor EIICBGlc is extremely complex. At least seven different proteins are involved in the transcriptional control (reviewed in [7]). Moreover, several research groups have identified and characterized the function of the sgrRST-system, which creates a sophisticated posttranscriptional feedback regulation mechanism of glucose transport during intracellular Glc6-P Inhibitors,research,lifescience,medical or Fru6-P accumulation [23,24,26,27,34,35]. Whereas the small regulatory RNA SgrS destabilizes ptsG m-RNA, the function of the small regulatory peptide SgrT, which is simultaneously encoded by the sgrS gene, has not been very well characterized thus far.

In this Inhibitors,research,lifescience,medical paper we could demonstrate for the first time by several experimental approaches, that the highly conserved KTPGRED motif in the linker region between the EIICGlc and the EIIBGlc domains of the glucose transporter constitutes the SgrT target site. Furthermore, using site-directed mutagenesis, we were able to identify the most important residues for this protein–protein interaction. Inhibitors,research,lifescience,medical These findings finally provide a good explanation for the existence of this highly conserved motif within an otherwise non-conserved region of the protein. Moreover, we could demonstrate that according to the physiological needs, almost exclusively dephosphorylated EIICBGlc

interacts with SgrT. During glucose uptake EIICBGlc conducts several conformational changes which result in glucose translocation and phosphorylation [36]. Glucose is bound with high affinity on the periplasmic site of the inner membrane. Subsequently, the protein conformation changes Inhibitors,research,lifescience,medical into an occluded state (the glucose is completely surrounded by the protein). Phosphorylation of the substrate again causes a conformational change and thus leads to a decreased affinity and to the release of Glc6-P into the cytoplasm [36]. Erni et al. could demonstrate that the flexible linker which connects the phosphorylated EIIBGlc-domain with the glucose binding EIICGlc-domain conducts severe conformational Inhibitors,research,lifescience,medical changes during this transport process

[10]. This provides an explanation for the clear differences observed others in SgrT binding between phosphorylated and unphosphorylated EIICBGlc. Furthermore, transport activity of EIICBGlc is influenced by different amino acid substitutions which can be dissected into three groups: The first group consists of mutations which cause “relaxed” substrate specificity. These single amino acid substitutions are scattered over the entire EIICGlc domain and allow facilitated diffusion of substrates like mannose and glucosamine [16,37], fructose [38], ribose and xylose [39], mannitol [40], ribitol und arabinitol, respectively (reviewed in [10]). In contrast, so-called “uncoupled” mutants exhibit a separation of translocation and phosphorylation and the uptake of unphosphorylated glucose, for example, in a ptsHICrr deletion background [29,41].