The ESX-1 type VII (T7SS) secretion system is an important determinant of virulence in pathogenic mycobacteria, including Mycobacterium tuberculosis. This complicated molecular machine secretes folded proteins through the mycobacterial cell envelope to subvert the host immune response. The protein EccB1, a core component of the T7SS, is an ATPase required for the secretion of virulence factors by the ESX-1 system. The periplasmic domain of EccB1 is itself comprised of five domains, 4 repeat domains and a central domain. Structural domains comprising this superfamily share the structure of the repeat 3 (R3) domain, which flanks this core domain. The repeat domains of EccB1 are structurally similar to a known peptidoglycan binding protein which suggest their role in anchoring the ESX-1 system within the periplasmic space PMID:26922638,PMID:26841765.