Part of the ESX-1 specialized secretion system, which delivers several virulence factors to host cells during infection, including the key virulence factors EsxA (ESAT-6) and EsxB (CFP-10). EsxB binding to the second FtsK domain of EccCb1 causes multimerization; a subsequent unknown step relieves the allosteric inhibition of linker 2 on FtsK domain 1 (this subunit), activating the ATPase activity (PubMed:25865481). Part of the ESX-1 / type VII secretion system (T7SS), which is composed of cytosolic and membrane components. The ESX-1 membrane complex is composed of EccB1, EccCa1, EccCb1, EccD1 and EccE1 (PubMed:14557536, PubMed:16368961, PubMed:19876390). Interacts with EccCb1 (PubMed:14557536). Residues 62-332 interact with EsxB and an artificial EsxB-EsxA heterodimer (PubMed:19854905). Disruption abolishes EsxA and EsxB secretion, but not their expression (PubMed:14557536). It results in a lack of antigen specific immunogenicity and leads to attenuated virulence (PubMed:16368961). Mutants exhibit defects in bacterial growth during the acute phase of a mouse infection (PubMed:14557536). No growth in the human macrophage-like cell line THP-1, no cytotoxicity; bacteria grow within cells but do not kill them and do not spread to other host cells (PubMed:14756778). In ESX-1 cluster, the FtsK/SpoIIIE-like protein is split in two genes.