Figure 9.

The CusABC system for Cu export. CusA is an integral membrane protein that binds two CusB copies to form a CusA₃-CusB₆ complex. The methionine triad for Cu/Ag binding in CusA is depicted in the insert. CusC is the outer membrane component that forms a trimer in the outer membrane and interacts with CusB. However, the complete structure of the CusA₃B₆C₃ complex has not been solved yet. The CusA₃B₆C₃ complex can transport Cu from the cytoplasm into the extracellular space but can also receive Cu from the periplasmic Cu chaperone CusF, which binds Cu via methionine and histidine residues (insert). Structures were retrieved from the protein database (PDB) with the following IDs: 3KSS (CusA), 3NE5 (CusBA), 4K7R (CusC), 2VB2 (CusF), and depicted using Pymol.