Beta-Barrel Channel Response to High Electric Fields: Functional Gating or Reversible Denaturation?

Area of Science:

• Biophysics
• Membrane protein structure and function
• Protein electrostatics

Background:

• Ion channels regulate cellular activity, with voltage-gated channels crucial for excitable cells.
• β-barrel channels, unlike α-helical channels, are less selective and not directly linked to cell excitability.
• These β-barrel channels can close under strong electric fields and reopen upon field removal, retaining a memory of the event.

Purpose of the Study:

• To investigate whether the voltage-induced closure of β-barrel channels is functional gating or reversible protein denaturation.
• To analyze the closing-opening process of the bacterial outer membrane channel OmpF in planar lipid bilayers.

Main Methods:

• Reconstitution of the bacterial outer membrane channel OmpF into planar lipid bilayers.
• Application of high electric fields (exceeding 20 million volts per meter) to induce channel closure.
• Analysis of channel closing-opening characteristics, including voltage polarity response, multiple closed states, channel clustering, gating memory, and Hofmeister effects.

Main Results:

• The observed characteristics of OmpF closure align with reversible protein denaturation rather than functional gating.
• Nearly symmetric response to voltages of both polarities suggests denaturation.
• Multiple closed states and long-term gating memory further support the denaturation hypothesis.
• Hofmeister effects on closing kinetics provide additional evidence for field-induced structural changes.

Conclusions:

• Voltage-induced closure of β-barrel channels like OmpF is likely a form of reversible protein denaturation by electric fields.
• This phenomenon may represent an evolutionary precursor to sophisticated voltage-gated channels found in nerve and muscle cells.