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The electron transport chain (ETC) is a crucial metabolic pathway that facilitates energy conversion in prokaryotic and eukaryotic cells. In eukaryotes, the ETC comprises four membrane-associated protein complexes in the inner mitochondrial membrane. In prokaryotes, the ETC in the plasma membrane can vary in composition, with fewer or different complexes depending on the organism and environmental conditions. These complexes transfer electrons from electron donors, such as NADH and FADH2, to...
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Voltage Sensing in Bacterial Protein Translocation.

Denis G Knyazev1, Roland Kuttner1, Ana-Nicoleta Bondar2

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Area of Science:

  • Membrane biology
  • Protein translocation
  • Molecular machinery

Background:

  • The SecYEG channel facilitates protein transport across bacterial membranes.
  • Its function is regulated by a plug and potentially membrane potential.
  • Existing models don't fully explain voltage-dependent gating.

Purpose of the Study:

  • To investigate the voltage-dependent gating mechanism of the SecYEG channel.
  • To identify the structural components responsible for voltage sensing.

Main Methods:

  • Purification and reconstitution of the SecYEG channel.
  • Electrophysiological recordings in the presence of ligands.
  • Site-directed mutagenesis of SecY transmembrane helix 2b (TM2b).

Main Results:

  • Demonstrated voltage-dependent channel closures in reconstituted SecYEG.
  • Identified TM2b as a key component of the voltage sensor.
  • Mutations in TM2b altered voltage sensitivity, supporting its role in gating.

Conclusions:

  • SecYEG channel gating is voltage-dependent.
  • TM2b, likely part of a larger sensor, contributes to voltage sensing through its dipole orientation.
  • Membrane potential influences channel closure by interacting with the TM2b-containing voltage sensor.