Chloride intracellular channel (CLIC) proteins function as fusogens

Area of Science:

• Molecular Biology
• Membrane Biophysics
• Protein Function

Background:

• Chloride Intracellular Channel (CLIC) proteins exhibit unique soluble and membrane-associated conformations.
• The precise physiological roles of CLICs, including their function as ion channels, remain incompletely understood.
• CLIC5's specific biological function has been a long-standing question in the field.

Purpose of the Study:

• To elucidate the functional role of CLIC5.
• To investigate the mechanism by which CLIC5 interacts with membranes.
• To determine the physiological relevance of CLIC5's membrane interactions.

Main Methods:

• Purification of CLIC5 protein.
• Liposome-based assays to measure membrane fusion (liposomal diameter, lipid, and content mixing).
• In vitro studies investigating pH-dependent activity and hydrophobic interface involvement.
• In vivo studies using C. elegans to assess the impact of CLIC5 mutations on development.

Main Results:

• Purified CLIC5 directly interacts with liposomes and induces membrane fusion.
• CLIC5-mediated fusion is enhanced at acidic pH and requires exposure of its hydrophobic inter-domain interface.
• Mutating a conserved hydrophobic residue in CLIC5 reduces its fusogenic activity in vitro and impairs C. elegans excretory canal extension in vivo.

Conclusions:

• CLIC5 functions as a membrane fusogen, providing a novel insight into CLIC protein activity.
• The fusogenic activity of CLIC5 is regulated by pH and specific protein structural features.
• This study unravels the physiological role of CLIC5, linking its membrane fusogenic function to biological development.