New insights into the interplay between the lysine transporter LysP and the pH sensor CadC in Escherichia coli.
The coordination of signal transduction and substrate transport represents a sophisticated way to integrate information on metabolite fluxes into transcriptional regulation. This widely distributed process involves protein-protein interactions between two integral membrane proteins. Here we report new insights into the molecular mechanism of the regulatory interplay between the lysine-specific permease LysP and the membrane-integrated pH sensor CadC, which together induce lysine-dependent adaptation of E. coli under acidic stress. In vivo analyses revealed that, in the absence of either stimulus, the two proteins form a stable association, which is modulated by lysine and low pH. In addition to its transmembrane helix, the periplasmic domain of CadC also participated in the interaction. Site-directed mutagenesis pinpointed Arg265 and Arg268 in CadC as well as Asp275 and Asp278 in LysP as potential periplasmic interaction sites. Moreover, a systematic analysis of 100 LysP variants with single-site replacements indicated that the lysine signal is transduced from co-sensor to sensor via lysine-dependent conformational changes (upon substrate binding and/or transport) of LysP. Our results suggest a scenario in which CadC is inhibited by LysP via intramembrane and periplasmic contacts under non-inducing conditions. Upon induction, lysine-dependent conformational changes in LysP transduce the lysine signal via a direct conformational coupling to CadC without resolving the interaction completely. Moreover, concomitant pH-dependent protonation of periplasmic amino acids in both proteins dissolves their electrostatic connections resulting in further destabilization of the CadC/LysP interaction.
Munich Center for Integrated Protein Science (CIPSM) at the Department of Microbiology, Ludwig-Maximilians-Universität München, 82152 Martinsried, Germany.
Martina
M
Rauschmeier
Munich Center for Integrated Protein Science (CIPSM) at the Department of Microbiology, Ludwig-Maximilians-Universität München, 82152 Martinsried, Germany.
Valentina
V
Schüppel
Munich Center for Integrated Protein Science (CIPSM) at the Department of Microbiology, Ludwig-Maximilians-Universität München, 82152 Martinsried, Germany.
Larissa
L
Tetsch
Munich Center for Integrated Protein Science (CIPSM) at the Department of Microbiology, Ludwig-Maximilians-Universität München, 82152 Martinsried, Germany. Electronic address: jung@lmu.de.
Kirsten
K
Jung
D026923:Amino Acid Transport Systems, Basic / Q000235:genetics / Q000378:metabolism*; D004252:DNA Mutational Analysis; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008239:Lysine / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D011485:Protein Binding; D025941:Protein Interaction Mapping; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*
D026923:Amino Acid Transport Systems, Basic; C087479:CadC protein, E coli; D029968:Escherichia coli Proteins; D015534:Trans-Activators; C430024:lysP protein, E coli; D008239:Lysine
ToxR-like transcriptional regulators; cadaverine; lysine decarboxylase; one-component system; signal transduction