3.A.24.1.1
The RD1 (ESX-1) protein secretion complex (Type VII protein secretion system, T7SS).  EccA1 may be a secreted protein while ECCB1 - E1 may comprise the system (Houben et al. 2012).  This system (ESX-1) is present in the avirulent species, Mycobacterium smegmatis, where it is involved in conjugation (Coros et al. 2008).  ESX-1 uses the ESX-1-specific chaparone protein, EspG to interact with the secreted PE/PPE complex, while a homologous EspG specific for ESX-5 functions with the PE/PPE complex secreted by ESX-5.  Thus, EspG proteins may be system-specific chaparones for T7SSs (Daleke et al. 2012).  The main secreted virulence protein complex is a heterodimer: EsxA(ESAT-6)/EsxB(CFP-10) (Rosenberger et al. 2012). EccB, a periplasmic homoheximer with the ATP-binding active site shared by two adjacent subunits, may act as the energy provider in the transport of T7SS virulence factors and may be involved in the formation of a channel across the mycomembrane (Zhang et al. 2015). ESX-1 functions in resistance to and evasion of host responses.  It induces phagosomal rupture which releases bacteria into the cytosol of the host phagocytes (Gröschel et al. 2016). ESX-1 secrete EsxA and EsxB, which form a heterodimer, seem to have differing functions as EsxA can disrupt lipid bilayers (RBC and artificial membranes.  Thus EsxA may form pores as a prelude to membrane disruption (Gröschel et al. 2016).