May help regulate assembly and function of the type VII secretion system (T7SS). Binds to EccC and induces its multimerization (PubMed:25865481). May serve as a chaperone for EsxA (By similarity). In isolation forms a homodimer (PubMed:25865481). Forms a tight 1:1 complex with EsxA (PubMed:25865481). Forms a complex with EsxA and EccC, probably wholly mediated by EsxB; binds in a pocket in the third FtsK (ATPase) domain of EccC (residues 1163-1208) (PubMed:25865481). Probably secreted via the ESX / type VII secretion system (T7SS). Belongs to the WXG100 family. CFP-10 subfamily.