Intracellular copper storage and delivery in a bacterium

Abstract

A family of cytosolic copper (Cu) storage proteins (the Csps) are widespread in bacteria. The Csps can bind large quantities of Cu(I) via their Cys-lined four-helix bundles, and the majority are cytosolic (Csp3s). This is inconsistent with the current dogma that bacteria, unlike eukaryotes, have evolved not to maintain intracellular pools of Cu due to its potential toxicity. Sporulation in Bacillus subtilis has been used to investigate if a Csp3 can store Cu(I) in the cytosol for a target enzyme. The activity of the Cu-requiring endospore multi-Cu oxidase BsCotA (a laccase) increases under Cu-replete conditions in wild type B. subtilis, but not in the strain lacking BsCsp3. Cuprous ions readily transfer from BsCsp3, but not from the cytosolic copper metallochaperone BsCopZ, to BsCotA in vitro producing active enzyme. Both BsCsp3 and BsCotA are upregulated during late sporulation. The hypothesis we propose is that BsCsp3 acquires and stores Cu(I) in the cytosol for BsCotA.