Part of the ESX-3 specialized secretion system, which is important for iron and zinc uptake or homeostasis. Part of the ESX-3 / type VII secretion system (T7SS), which is composed of cytosolic and membrane components. The ESX-3 membrane complex is composed of EccB3, EccC3, EccD3 and EccE3. Repressed by IdeR in the presence of iron and by Zur in the presence of zinc. Was identified as a high-confidence drug target. Belongs to the EccD/Snm4 family.