A CLC chloride channel plays an essential role in copper homeostasis in Aspergillus nidulans at increased extracellular copper concentrations

Abstract

A putative CLC voltage-gated anion channel gene from Aspergillus nidulans ( AnCLCA) is characterised. The expression of the AnCLCA cDNA restored the iron-limited growth of the Saccharomyces cerevisiae CLC null mutant strain ( gef1) suggesting that AnCLCA functions as a chloride channel. An AnCLCA conditional mutant was created and exhibited a strong and specific growth inhibition in the presence of extracellular copper concentrations > 18 μM. This sensitivity was shown to be the result of a hyper-accumulation of copper by the conditional mutant, which generates superoxide to toxic levels inhibiting the growth. Further analysis revealed that copper dependent enzymes were disrupted in the AnCLCA conditional null mutant, specifically, a reduced activity of the copper–zinc superoxide dismutase (CuZn–SOD) and enhanced activity of the cytochrome oxidase (COX). These results suggest that AnCLCA plays a key role in copper homeostasis in A. nidulans and that a malfunction of this chloride channel results in disrupted intracellular copper trafficking.