The CcmD protein is part of a C-type cytochrome biogenesis operon [1]. The exact function of this protein is uncertain. It has been proposed that CcmC, CcmD and CcmE interact directly with each other, establishing a cytoplasm to periplasm haem delivery pathway for cytochrome c maturation [2]. This protein is found fused to CcmE in Swiss:P52224. These proteins contain a predicted transmembrane helix.

1: Escherichia coli genes required for cytochrome c maturation. Thony-Meyer L, Fischer F, Kunzler P, Ritz D, Hennecke H; J Bacteriol 1995;177:4321-4326. PMID:7635817

2: New insights into the role of CcmC, CcmD and CcmE in the haem delivery pathway during cytochrome c maturation by a complete mutational analysis of the conserved tryptophan-rich motif of CcmC. Schulz H, Pellicioli EC, Thony-Meyer L; Mol Microbiol 2000;37:1379-1388. PMID:10998170