미생물생리학 연구실

In most bacteria, glucose and many other carbohydrates are transported via the phosphoenolpyruvate (PEP):sugar phosphotransferase system (PTS). This multi-component system carries out a PEP-dependent transport and phosphorylation of numerous sugars (group translocation; Fig. 1). There is a sequential phosphoryl transfer to two general proteins, enzyme I (EI) and HPr, then to membrane-associated enzymes II, which may consist of 3–4 domains (A, B, C, and D). Over the years, this system has become established as a central component in bacterial physiology as a result of the identification of multiple regulatory functions, superimposed on the transport functions, for essentially all the components of the glucose arm of the PTS (Fig. 2). Fig. 1. PEP:sugar phosphotransferase systems in E. coli. Fig. 2. PTS-mediated regulation of carbon metabolism in E. coli. Analysis of the Escherichia coli genome has revealed new phosphotransferase-encoding genes. The novel nitrogen-metabolic phosphotransferase system (PTSNtr) proteins, NPr and EIIANtr (paralogues of HPr and EIIAFru, respectively), are encoded by the ptsO and ptsN genes, respectively, localized to the rpoN operon of E. coli. Enzyme INtr (EINtr; enzyme I paralogue) encoded by the ptsP gene, located distant from the rpoN cluster on the chromosome, consists of two domains, an N-terminal domain of 127 amino acids homologous to the N-terminal sensory domain of the NifA protein of Azotobacter vinelandii and a C-terminal domain of 578 amino acids homologous to all currently sequenced enzymes I. It was shown that the E. coli nitrogen-metabolic PTS consists of the following phosphoryl transfer chain, PEP→EINtr→NPr→EIIANtr (Fig. 3). Because phosphoryl transfer to a specific substrate has not yet been demonstrated for the PTSNtr, it ha