Heme chaperone required for the biogenesis of c-type cytochromes. Transiently binds heme delivered by CcmC and transfers the heme to apo-cytochromes in a process facilitated by CcmF and CcmH. Forms a ternary complex with CcmC and CcmD. Interacts with CcmF. Shuttles between CcmC and CcmF for heme delivery. Stabilized by CcmD in the membrane. Belongs to the CcmE/CycJ family.