FIG 8.

Model for heme attachment by CcsBA. (A) Heme is stereospecifically positioned in the WWD domain, liganded by P-His1 and P-His2 with the heme vinyl groups surface exposed to the periplasm. (B) The CXXCH motif of apocyt c is positioned near heme, allowing exchange of P-His1 for the new His ligand and thioether formation between the cysteine thiols and heme vinyl groups. (C) Heme, covalently attached to the CXXCH motif, is released from the WWD domain. (D) Cyt c folds around the heme. Note that the known human cytochrome c (PDB 3ZCF, chain D) was used for illustrative purposes.