Copper delivery to an endospore coat protein of .

A family of cytosolic copper (Cu) storage proteins (the Csps) bind large quantities of Cu(I) via their Cys-lined four-helix bundles, and the majority are cytosolic (Csp3s). The presence of Csp3s in many bacteria appears 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 has been used to investigate if a Csp3 binds Cu(I) in the cytosol for a target enzyme. The activity of the Cu-requiring endospore multi-Cu oxidase CotA (a laccase) increases under Cu-replete conditions in wild type . In the strain lacking Csp3 lower CotA activity is observed and is unaffected by Cu levels. Csp3 loaded with Cu(I) readily activates apo-CotA . Experiments with a high affinity Cu(I) chelator demonstrate that Cu(I) transfer from Cu(I)-Csp3 must occur via an associative mechanism. Csp3 and CotA are both upregulated during late sporulation. We hypothesise that Csp3 acquires cuprous ions in the cytosol of for CotA.