title: The allosteric regulatory mechanism of the Escherichia coli MetNI methionine ATP binding cassette (ABC) transporter.
abstract: The MetNI methionine importer of Escherichia coli, an ATP binding cassette (ABC) transporter, uses the energy of ATP binding and hydrolysis to catalyze the high affinity uptake of D- and L-methionine. Early in vivo studies showed that the uptake of external methionine is repressed by the level of the internal methionine pool, a phenomenon termed transinhibition. Our understanding of the MetNI mechanism has thus far been limited to a series of crystal structures in an inward-facing conformation. To understand the molecular mechanism of transinhibition, we studied the kinetics of ATP hydrolysis using detergent-solubilized MetNI. We find that transinhibition is due to noncompetitive inhibition by L-methionine, much like a negative feedback loop. Thermodynamic analyses revealed two allosteric methionine binding sites per transporter. This quantitative analysis of transinhibition, the first to our knowledge for a structurally defined transporter, builds upon the previously proposed structurally based model for regulation. This mechanism of regulation at the transporter activity level could be applicable to not only ABC transporters but other types of membrane transporters as well.
authors: From the Division of Chemistry and Chemical Engineering and the Howard Hughes Medical Institute, California Institute of Technology, Pasadena, California 91125.
authors: Janet G
authors: JG
authors: Yang
authors: From the Division of Chemistry and Chemical Engineering and the Howard Hughes Medical Institute, California Institute of Technology, Pasadena, California 91125 dcrees@caltech.edu.
authors: Douglas C
authors: DC
authors: Rees
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000378:metabolism*; D000494:Allosteric Regulation; D002151:Calorimetry; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000378:metabolism*
chemical_list: D018528:ATP-Binding Cassette Transporters; D029968:Escherichia coli Proteins
keywords: ABC Transporter; ATPase; Amino Acid Transport; Enzyme Mechanism; Methionine