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Subconductance states in OmpF gating.

Arnaud Baslé1, Ram Iyer, Anne H Delcour

  • 1Department of Biology and Biochemistry, University of Houston, 369 Science and Research Building 2, Houston, TX 77204-5001, USA.

Biochimica Et Biophysica Acta
|July 9, 2004
PubMed
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Discrepancies in Escherichia coli porin OmpF conductance measurements were resolved by comparing black lipid membrane and patch clamp techniques. Subconductance states were universally observed, with polyamines significantly enhancing gating behavior.

Area of Science:

  • Biophysics
  • Molecular Biology
  • Membrane Protein Research

Background:

  • Published conductance values for Escherichia coli porin OmpF show significant discrepancies.
  • Variations in experimental conditions, including channel preparation, salt type/concentration, and electrophysiological techniques (black lipid membrane vs. patch clamp), hinder direct comparison of OmpF data.
  • A unified understanding of OmpF porin behavior is lacking due to these inconsistencies.

Purpose of the Study:

  • To reconcile conflicting published data on Escherichia coli OmpF porin conductance.
  • To present a side-by-side comparison of OmpF activity using black lipid membrane and patch clamp techniques on identical protein preparations and under consistent experimental conditions (150 mM KCl).
  • To investigate the role of polyamines in modulating OmpF porin gating behavior.

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Main Methods:

  • Purification of Escherichia coli OmpF porin.
  • Electrophysiological recordings using both black lipid membrane (BLM) and patch clamp techniques.
  • Comparative analysis of OmpF channel activity under identical low salt concentrations (150 mM KCl).
  • Investigation of OmpF gating in the presence of polyamines, specifically spermine.

Main Results:

  • The study revealed the ubiquitous presence of subconductance states (smaller conductance than monomeric) for OmpF porin, irrespective of the technique or conditions used.
  • Subconductance gating was found to be significantly enhanced by polyamines, particularly spermine, leading to more frequent and prolonged occupation of these substates.
  • Monomeric closures of OmpF were observed to be rare at clamped potentials below approximately 100-120 mV, with subconductance gating dominating channel activity.

Conclusions:

  • Subconductance states represent a fundamental and previously underappreciated aspect of OmpF porin behavior.
  • Polyamines play a crucial role in modulating OmpF porin gating, significantly increasing the occurrence and duration of subconductance states.
  • The findings provide a basis for understanding the molecular mechanisms underlying porin gating and reconciling disparate experimental observations.