Part of the ESX specialized secretion system, which exports proteins from the cell including EsxA (ESAT-6) and EsxB (CFP-10) (By similarity). Might be the translocase subunit (PubMed:25865481). Probably only the first FtsK domain can hydrolyze ATP (PubMed:27130157). EsxB binding to the third FtsK domain causes multimerization; a subsequent unknown step relieves the allosteric inhibition of linker 2 on FtsK domain 1, activating the ATPase activity (By similarity). Whole protein oligomerizes in native gels (PubMed:27130157). Part of the ESX / type VII secretion system (T7SS), which is composed of cytosolic and membrane components. The ESX membrane complex is composed of EccB, EccC and EccD (By similarity). The cytoplasmic domain is a rigid structure with 4 domains (residues 480 to 599 form an unnamed domain) plus the 3 FtsK (ATPase) domains which are connected by short linkers (PubMed:25865481). Unlike the well characterized M.tuberculosis ESX-1 cluster, this protein is not split into 2 genes. This subunit and a WGX100 family protein are the only proteins universally associated with T7SS.