A Zn(2+)-triggered two-step mechanism of CLIC1 membrane insertion and activation into chloride channels

The chloride intracellular channel (CLIC) protein family displays the unique feature of altering its structure from a soluble form to a membrane-bound chloride channel. CLIC1, a member of this family, is found in the cytoplasm or in internal and plasma membranes, with membrane relocalisation linked to endothelial disfunction, tumour proliferation and metastasis. The molecular switch promoting CLIC1 activation remains under investigation. Here, cellular Cl(−) efflux assays and immunofluorescence microscopy studies have identified intracellular Zn(2+) release as the trigger for CLIC1 activation and membrane insertion. Biophysical assays confirmed specific binding to Zn(2+), inducing membrane association and enhancing Cl(−) efflux in a pH-dependent manner. Together, our results identify a two-step mechanism with Zn(2+) binding as the molecular switch promoting CLIC1 membrane insertion, followed by pH-mediated activation of Cl(−) efflux.