Carboxy-terminal truncations modify the outer pore vestibule of muscle chloride channels

Area of Science:

• Molecular biology
• Biophysics
• Ion channel research

Background:

• Mammalian ClC-type chloride channels possess large, functionally uncharacterized cytoplasmic carboxy-terminal domains.
• The muscle isoform, ClC-1, is crucial for muscle membrane potential and function.

Purpose of the Study:

• To investigate the role of the distal carboxy-terminus of the muscle ClC-1 chloride channel.
• To determine how truncations in this domain affect channel function, including ion permeation and gating.

Main Methods:

• Construction and functional evaluation of two ClC-1 truncation mutants (R894X and K875X).
• Assessment of unitary conductances, anion selectivities, and apparent anion binding affinities.
• Analysis of voltage-dependent gating kinetics and methanethiosulphonate (MTS) modification rates.

Main Results:

• Truncated ClC-1 channels retained normal unitary conductances and anion selectivities.
• Altered apparent anion binding affinities were observed in both open and closed states of truncated channels.
• Changes in pore properties led to modified fast and slow gating kinetics.
• Differences in MTS modification rates at cysteine 231 were noted between full-length and truncated channels.

Conclusions:

• The carboxy-terminus of ClC-1 channels significantly impacts the outer pore vestibule conformation.
• This conformational modification influences ion binding and voltage-dependent gating.
• The distal carboxy-terminus plays a critical role in regulating ClC-1 channel function.