Cooperativity and Steep Voltage Dependence in a Bacterial Channel

Area of Science:

• Biophysics
• Molecular Biology
• Membrane Protein Research

Background:

• Ion channels are crucial for cellular function.
• Understanding novel channel structures is key to deciphering biological processes.
• Escherichia coli harbors diverse membrane proteins with unique functions.

Purpose of the Study:

• To report the discovery and characterization of a novel three-membrane channel unit.
• To investigate the voltage dependence and cooperative behavior of this new channel.
• To elucidate the potential physiological significance of the novel channel structure.

Main Methods:

• Reconstitution of the channel-former into planar phospholipid membranes.
• Voltage-clamp electrophysiology to study channel behavior.
• Analysis of voltage dependence and cooperative gating mechanisms.

Main Results:

• Discovery of a novel three-membrane channel unit, named "triplin," from Escherichia coli.
• Observed very steep voltage dependence, indicating a substantial voltage sensor (≥14 charges).
• Demonstrated strong cooperative gating: channel closure of one unit facilitates the closure of the next.
• Identified differential gating at positive and negative potentials, suggesting an opposing orientation for the second channel unit.

Conclusions:

• Triplin exhibits unique gating properties, including steep voltage dependence and cooperativity, comparable to mammalian excitable membrane channels.
• The observed differential gating suggests a specific transmembrane orientation of the channel units.
• Triplin's extraordinary behavior points to important, yet undefined, physiological roles in Escherichia coli.