FIG 6 .

Schematic comparison of Cu_B incorporation into the active sites of bacterial aa₃- and cbb₃-Cox. A complete understanding of the pathways of Cu uptake and delivery to the heme-Cu_B binuclear site of HCOs is still missing. All known components involved in the biogenesis of the Cu_B center of bacterial aa₃- and cbb₃-Cox are depicted. In the case of aa₃-Cox, the Cox1 subunit is thought to receive Cu_B from the Cu chaperone Cox11 either directly or via an unknown partner(s). How Cu is initially conveyed to Cox11 remains unknown. A putative Cu importer of unknown identity (black box) that is possibly functionally similar to mitochondrial Pic2 (71) is included. In the case of cbb₃-Cox, Cu is imported by CcoA and is conveyed by the CcoGHIS, PCuAC, and PrrC (PccA and SenC homologs) assembly components to the Cu_B site of the CcoN subunit by a mechanism that remains elusive. Question marks indicate unknown Cu transfer steps.