Periplasmic competition for zinc uptake between the metallochaperone ZnuA and Cu,Zn superoxide dismutase.

We have investigated the availability of zinc in the periplasmic space of Escherichia coli using a mutant Cu,Zn superoxide dismutase whose dimerization is triggered by zinc binding. This mutant enzyme accumulates in the monomeric form when wild type cells are grown in minimal medium, but assembles in the dimeric form when it is produced in the same medium by a mutant strain lacking the periplasmic zinc metallochaperone ZnuA. These results indicate that periplasmic zinc-containing proteins compete for metal binding when bacteria grow in environments where this element is present in traces. The effective ZnuA ability to sequester the available zinc ions from the periplasm suggests that zinc-containing cytoplasmic proteins are more important for bacterial viability than the periplasmic ones.