Metal transporters that contribute copper to metallochaperones in Saccharomyces cerevisiae

Copper metallochaperones represent a new family of soluble, low-molecular-w eight proteins that function to deliver copper to specific sites within a c ell. How the metallochaperones acquire their copper, however, is not known. In this study, we have conducted a survey of known metal ion transporters in bakers' yeast, Saccharomyces cerevisiae, to identify those that contribu te copper to pathways involving the metallochaperones Atx1p and Lys7p. The results indicate that, in addition to the well known Ctr1p and Ctr3p high-a ffinity copper transporters, the metallochaperones can acquire their copper through pathways involving the relatively non-specific divalent metal ion transporter Fet4p and the putative low-affinitycopper transporter Ctr2p. We have examined the localization of Ctr2p using an epitope tagged version of the protein and find that Ctr2p does not localize to the cell surface but may operate at the level of the vacuole to mobilize intracellular copper. I naddition to Ctr1p, Ctr2p, Ctr3p and Fet4p, other metal transport systems c an act as upstream donors of copper for the metallochaperones when copper a vailability in the medium is increased. Although the nature of these auxili ary systems is unknown, they donot appear to involve the yeast members of t he Nramp family of divalent transporters, or uptake mechanisms that involve endocytosis. Since vastly different metal transporters located at either t he cell surface or intracellular sites can all contribute copper to metallo chaperones, it is unlikely that the metallochaperones directly interact wit h the metal transporters to obtain the metal.