Molecular determinants underlying volume-regulated anion channel subunit-dependent oxidation sensitivity

Area of Science:

• Cellular Biology
• Molecular Mechanisms
• Ion Channel Function

Background:

• Volume-regulated anion channels (VRACs), formed by LRRC8 subunits, are crucial for cell homeostasis.
• VRACs play a significant role in oxidative stress responses, directly modulated by reactive oxygen species (ROS).
• Different LRRC8 heteromeric channel compositions exhibit opposing responses to oxidation: LRRC8A-LRRC8E channels are activated, while LRRC8A-LRRC8C channels are inhibited.

Purpose of the Study:

• To identify specific amino acid residues responsible for the differential oxidation-dependent regulation of LRRC8A-LRRC8E and LRRC8A-LRRC8C heteromeric channels.
• To elucidate the molecular mechanisms underlying VRAC channel activation and inhibition by oxidants.

Main Methods:

• Chimeric and concatemeric strategies were employed to map functional domains within LRRC8 subunits.
• Site-directed mutagenesis and biochemical assays were used to identify and characterize critical cysteine and methionine residues.
• Investigated the effect of oxidation on channel activity and conformational changes.

Main Results:

• Two specific cysteines (C424 and C448) in the leucine-rich repeats of LRRC8E were identified as oxidation targets, forming a disulfide bond that activates LRRC8A-LRRC8E channels.
• Oxidation of the first methionine residue in LRRC8C was identified as the cause of LRRC8A-LRRC8C channel inhibition.
• The inhibitory effect on LRRC8A-LRRC8C channels is dependent on the specific leucine-rich repeat (LRR) domain identity.

Conclusions:

• Identified key molecular determinants (C424, C448 in LRRC8E; first methionine in LRRC8C) governing the subunit-specific response of VRACs to oxidative stress.
• Provided crucial insights into the structural basis of ROS modulation of VRAC channels, relevant for understanding physiological ROS effects.
• Highlighted the importance of specific amino acid residues and their redox state in regulating ion channel function and cellular responses to oxidative stress.