Members of the chloride intracellular ion channel protein family demonstrate glutaredoxin-like enzymatic activity

PLoS One. 2015 Jan 12;10(1):e115699. doi: 10.1371/journal.pone.0115699. eCollection 2015.


The Chloride Intracellular Ion Channel (CLIC) family consists of six evolutionarily conserved proteins in humans. Members of this family are unusual, existing as both monomeric soluble proteins and as integral membrane proteins where they function as chloride selective ion channels, however no function has previously been assigned to their soluble form. Structural studies have shown that in the soluble form, CLIC proteins adopt a glutathione S-transferase (GST) fold, however, they have an active site with a conserved glutaredoxin monothiol motif, similar to the omega class GSTs. We demonstrate that CLIC proteins have glutaredoxin-like glutathione-dependent oxidoreductase enzymatic activity. CLICs 1, 2 and 4 demonstrate typical glutaredoxin-like activity using 2-hydroxyethyl disulfide as a substrate. Mutagenesis experiments identify cysteine 24 as the catalytic cysteine residue in CLIC1, which is consistent with its structure. CLIC1 was shown to reduce sodium selenite and dehydroascorbate in a glutathione-dependent manner. Previous electrophysiological studies have shown that the drugs IAA-94 and A9C specifically block CLIC channel activity. These same compounds inhibit CLIC1 oxidoreductase activity. This work for the first time assigns a functional activity to the soluble form of the CLIC proteins. Our results demonstrate that the soluble form of the CLIC proteins has an enzymatic activity that is distinct from the channel activity of their integral membrane form. This CLIC enzymatic activity may be important for protecting the intracellular environment against oxidation. It is also likely that this enzymatic activity regulates the CLIC ion channel function.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Chloride Channels / metabolism*
  • Glutaredoxins / metabolism*
  • Glutathione Transferase / metabolism
  • Models, Molecular
  • Protein Conformation*
  • Protein Structure, Tertiary


  • Chloride Channels
  • GLRX protein, human
  • Glutaredoxins
  • Glutathione Transferase

Grant support

The authors thank the following organisations for financial support of this research: the Centre for Health Technologies, University of Technology Sydney (funding support to SMV); the Australian Research Council (grant LP120200078 to SMV and BAC) and the Australian Institute of Nuclear Science and Engineering (AINSE Award to SMV, HA, KRH). ARC website URL:; AINSE website URL: The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.