期刊
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
卷 108, 期 43, 页码 E890-E898出版社
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1109597108
关键词
atomic force microscopy; energy landscape; membrane transporter; osmoregulation; secondary substrate-binding site
资金
- Deutsche Forschungsgemeinschaft (DFG)
- Bundesministerium fur Bildung und Forschung (BMBF)
- European Union
- Swiss National Science Foundation (SNF)
- DFG Collaborative Research Center
BetP, a trimeric Na+-coupled betaine symporter, senses hyperosmotic stress via its cytoplasmic C-terminal domain and regulates transport activity in dependence of the cytoplasmic K+-concentration. This transport regulation of BetP depends on a sophisticated interaction network. Using single-molecule force spectroscopy we structurally localize and quantify these interactions changing on K+-dependent transport activation and substrate-binding. K+ significantly strengthened all interactions, modulated lifetimes of functionally important structural regions, and increased the mechanical rigidity of the symporter. Substrate-binding could modulate, but not establish most of these K+-dependent interactions. A pronounced effect triggered by K+ was observed at the periplasmic helical loop EH2. Tryptophan quenching experiments revealed that elevated K+-concentrations akin to those BetP encounters during hyperosmotic stress trigger the formation of a periplasmic second betaine-binding (S2) site, which was found to be at a similar position reported previously for the BetP homologue CaiT. In BetP, the presence of the S2 site strengthened the interaction between EH2, transmembrane alpha-helix 12 and the K+-sensing C-terminal domain resulting in a K+-dependent cooperative betaine-binding.
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