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

Heba Al Khamici; Louise J Brown; Khondker R Hossain; Amanda L Hudson; Alxcia A Sinclair-Burton; Jane Phui Mun Ng; Elizabeth L Daniel; Joanna E Hare; Bruce A Cornell; Paul M G Curmi; Mary W Davey; Stella M Valenzuela

doi:10.1371/journal.pone.0115699

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.

Affiliations

¹ School of Medical and Molecular Biosciences, University of Technology Sydney, Sydney, New South Wales 2007, Australia.
² Department of Chemistry and Bimolecular Sciences, Macquarie University, Sydney, New South Wales 2109, Australia.
³ School of Medical and Molecular Biosciences, University of Technology Sydney, Sydney, New South Wales 2007, Australia; Bragg Institute, Australian Nuclear Science and Technology Organisation, Sydney, New South Wales 2234, Australia.
⁴ Surgical Diagnostics, Roseville, Sydney, New South Wales 2069, Australia.
⁵ School of Physics, University of New South Wales, Sydney, New South Wales 2052, Australia; Centre for Applied Medical Research, St Vincent's Hospital, Sydney, New South Wales 2010, Australia.
⁶ School of Medical and Molecular Biosciences, University of Technology Sydney, Sydney, New South Wales 2007, Australia; Centre for Health Technologies, University of Technology Sydney, Sydney, New South Wales 2007, Australia.

Abstract

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

Substances

Chloride Channels
GLRX protein, human
Glutaredoxins
Glutathione Transferase

Grants and funding

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: http://www.arc.gov.au/; AINSE website URL: http://www.ainse.edu.au/. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.