3.A.3.5.38
Cuprous ion (Cu⁺) exporter, CopB, of 785 aas and 8 TMSs in a 4 + 2 + 2 arrangement. The copper-transporting P1B-ATPases have been divided traditionally into two subfamilies, the P1B-1-ATPases or CopAs and the P1B-3-ATPases or CopBs. CopAs selectively export Cu⁺ whereas previous studies have suggested that CopBs are specific for Cu²⁺ export. Biochemical and spectroscopic characterization of Sphaerobacter thermophilus CopB (StCopB) showed that, while it does bind Cu²⁺, the binding site is not in the transmembrane domain (Purohit et al. 2018).  StCopB exhibits metal-stimulated ATPase activity in response to Cu⁺, but not Cu²⁺, indicating that it is actually a Cu⁺ transporter. Cu⁺ is coordinated by four sulfur ligands derived from conserved cysteine and methionine residues. The histidine-rich N-terminal region is required for maximal activity, but is inhibitory in the presence of divalent metal ions. P1B-1- and P1B-3-ATPases may therefore all transport Cu⁺ (Purohit et al. 2018).