Cu + -specific CopB transporter: Revising P 1B -type ATPase classification

Significance Copper is an important biological cofactor, but can also be toxic in excess. Members of the P 1B -ATPase family of membrane transporters couple the energy of ATP hydrolysis to translocation of metal ions across membranes. P 1B -ATPases have been classified into groups on the basis of sequence and metal ion specificity. Two subfamilies, the P 1B-1 -ATPases, which are linked to human diseases of copper metabolism, and the P 1B-3 -ATPases, found only in bacteria, have been assigned as Cu + and Cu 2+ transporters, respectively. Here we show that the P 1B-3 -ATPases are actually Cu + transporters, necessitating revision of the classification scheme. These findings are consistent with the presence of only Cu + in the cytoplasm, which eliminates the need for a Cu 2+ efflux pump.