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New insights into the interplay between the lysine transporter LysP and the pH sensor CadC in Escherichia coli.

J. Mol. Biol.2014 Jan 9;426(1):215-29. Epub 2013 Sep 20
Martina Rauschmeier 1 , Valentina Schüppel 1 , Larissa Tetsch 1 , Kirsten Jung 2
Martina Rauschmeier 1 , Valentina Schüppel 1 , Larissa Tetsch 1 , Kirsten Jung 2

[No authors listed]

Author information
  • 1 Munich Center for Integrated Protein Science (CIPSM) at the Department of Microbiology, Ludwig-Maximilians-Universität München, 82152 Martinsried, Germany.
  • 2 Munich Center for Integrated Protein Science (CIPSM) at the Department of Microbiology, Ludwig-Maximilians-Universität München, 82152 Martinsried, Germany. Electronic address: jung@lmu.de.

摘要


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.

KEYWORDS: ToxR-like transcriptional regulators, cadaverine, lysine decarboxylase, one-component system, signal transduction