Metallochaperones, an intracellular shuttle service for metal ions

Enzymes that employ transition metals as co-factors are housed in a wide va riety of intracellular locations or are exported to the extracellular milie u. A key question then arises: how are specific metal co-factors transporte d to diverse locations and subsequently sorted into the correct metalloenzy mes? The mechanisms by which these tasks are accomplished are just now bein g unraveled. A new family of soluble metal receptor proteins known as "meta llochaperones" is emerging that act in the intracellular trafficking of met al ions. Although transition elements can be quite toxic, these metal recep tors are not detoxification proteins; they clearly function in a "chaperone -like" manner, guiding and protecting the metal ion while facilitating appr opriate partnerships. Here we will review the most recent advances in our u nderstanding of copper metallochaperones and discuss mechanisms that may be relevant to other essential, yet potentially toxic, metal ions.