Topography of the Surface of the Signal-transducing Protein EIIAGlc That Interacts with the MalK Subunits of the Maltose ATP-binding Cassette Transporter (MalFGK2) of Salmonella typhimurium

Abstract

The signal-transducing protein EIIAGlc, a component of the phosphoenolpyruvate-glucose phosphotransferase system, plays a key role in carbon regulation in enteric bacteria, such as Escherichia coli and Salmonella typhimurium. The phosphorylation state of EIIAGlc governs transport and metabolism of a number of carbohydrates. When glucose as preferred carbon source is transported, EIIAGlc becomes predominantly unphosphorylated and allosterically inhibits several permeases, including the maltose ATP-binding cassette transport system (MalFGK2) in a process termed “inducer exclusion.” We have mapped the binding surface of EIIAGlc that interacts with the MalK subunits by using synthetic cellulose-bound peptide arrays like pep scan- and substitutional analyses. Three regions constituting two binding sites were identified encompassing residues 69-79 (I), 87-91 (II), and 118-127 (III). Region III is MalK-specific, whereas residues from regions I and II partly overlap but are not identical to the binding interfaces for interaction with glycerol kinase and lactose permease. These results were fully verified by studying the inhibitory effect of purified EIIAGlc variants carrying mutations at positions representative of each of the three regions on the ATPase activity of the purified maltose transport complex reconstituted into proteoliposomes. Moreover, a synthetic peptide encompassing residues 69-91 was demonstrated to partially inhibit ATPase activity. We also show for the first time that the N-terminal domain of EIIAGlc is essential for inducer exclusion. The signal-transducing protein EIIAGlc, a component of the phosphoenolpyruvate-glucose phosphotransferase system, plays a key role in carbon regulation in enteric bacteria, such as Escherichia coli and Salmonella typhimurium. The phosphorylation state of EIIAGlc governs transport and metabolism of a number of carbohydrates. When glucose as preferred carbon source is transported, EIIAGlc becomes predominantly unphosphorylated and allosterically inhibits several permeases, including the maltose ATP-binding cassette transport system (MalFGK2) in a process termed “inducer exclusion.” We have mapped the binding surface of EIIAGlc that interacts with the MalK subunits by using synthetic cellulose-bound peptide arrays like pep scan- and substitutional analyses. Three regions constituting two binding sites were identified encompassing residues 69-79 (I), 87-91 (II), and 118-127 (III). Region III is MalK-specific, whereas residues from regions I and II partly overlap but are not identical to the binding interfaces for interaction with glycerol kinase and lactose permease. These results were fully verified by studying the inhibitory effect of purified EIIAGlc variants carrying mutations at positions representative of each of the three regions on the ATPase activity of the purified maltose transport complex reconstituted into proteoliposomes. Moreover, a synthetic peptide encompassing residues 69-91 was demonstrated to partially inhibit ATPase activity. We also show for the first time that the N-terminal domain of EIIAGlc is essential for inducer exclusion. Complex bacterial activities, like those involved in the quest of food, require the coordination of entire metabolic networks. In enteric bacteria, such as Escherichia coli and Salmonella typhimurium, the phosphoenolpyruvate carbohydrate phosphotransferase system (PTS) 2The abbreviations used are: PTS, phosphoenolpyruvate carbohydrate phosphotransferase system; Ni-NTA, nickel nitrilotriacetic acid; TBS, Tris-buffered saline. plays a key role in this process as a signal transduction system (1Lengeler J.W. Jahreis K. Handbook of Biological Physics. Elsevier, Amsterdam1996Google Scholar). The PTS comprises a cascade of protein kinases and phosphocarriers that constitute a series of transport systems, which couple transport and phosphorylation of numerous sugars. The pathway requires the sequential transfer of a phosphoryl group from phosphoenolp