| Summary: | ATP-binding cassette (ABC) transporters couple ATP hydrolysis to import and export of a large array of substances across cell membranes in all kingdoms of life. Since the transport reaction consumes cellular energy, substrate translocation mediated by ABC transporters must be regulated according to the requirements of the cell. This thesis uses the Escherichia coli maltose transporter MalFGK2 to understand the regulatory mechanisms of ABC importers. Biochemical and biophysical approaches were employed to investigate how this transport process is modulated by maltose, the maltose-binding protein MalE and the glucose-specific enzyme EIIAGlc. First, I show that ATP facilitates MalE binding to MalFGK2, which forms the complex of MalE-MalFGK2 for efficient maltose transport. In addition, when the external maltose level exceeds that required, maltose is able to limit the maximal transport rate by promoting dissociation of MalE from MalFGK2. Finally, I find that the N-terminal tail of EIIAGlc and acidic phospholipids are essential for the binding of the protein to the MalK dimer, so that cleavage of ATP by MalFGK2 is inhibited. These results, combined with previous genetic, biochemical and structural work, provide valuable insights into our understanding of the regulatory mechanisms of the maltose transport system. === Medicine, Faculty of === Biochemistry and Molecular Biology, Department of === Graduate
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