Mycobacterial ESX-1 secretion system mediates host cell lysis through bacterium contact-dependent gross membrane disruptions

Abstract

Mycobacterium tuberculosis and Mycobacterium marinum are thought to exert virulence, in part, through their ability to lyse host cell membranes. The type VII secretion system ESX-1 [6-kDa early secretory antigenic target (ESAT-6) secretion system 1] is required for both virulence and host cell membrane lysis. Both activities are attributed to the pore-forming activity of the ESX-1-secreted substrate ESAT-6 because multiple studies have reported that recombinant ESAT-6 lyses eukaryotic membranes. We too find ESX-1 of M. tuberculosis and M. marinum lyses host cell membranes. However, we find that recombinant ESAT-6 does not lyse cell membranes. The lytic activity previously attributed to ESAT-6 is due to residual detergent in the preparations. We report here that ESX-1-dependent cell membrane lysis is contact dependent and accompanied by gross membrane disruptions rather than discrete pores. ESX-1-mediated lysis is also morphologically distinct from the contact-dependent lysis of other bacterial secretion systems. Our findings suggest redirection of research to understand the mechanism of ESX-1-mediated lysis.Mycobacterium tuberculosis | Mycobacterium marinum | ESAT-6 | ESX-1 secretion system | cell membrane lysis

Esx Systems and the Mycobacterial Cell Envelope: What's the Connection?

“…Although EsxA appears to be insufficient to promote ESX-1-mediated membrane lysis, the study by Conrad et al definitively showed that the M. marinum ESX-1 system functions to lyse membranes in a contact-dependent manner (182). Contact-dependent membrane lysis by mycobacteria has been suggested but not directly demonstrated in several earlier studies (44,167,184).…”

“…Conrad et al found undeniably that EsxA is not sufficient to promote membrane lysis (182). Recombinant EsxA is widely acquired directly from the BEI repository or produced using a nondenaturing protocol, which includes the addition of detergent (183).…”

“…Although the authors observed pH-dependent lytic activity of recombinant EsxA prepared without detergent, they show that changes in pH are not required to mediate ESX-1-mediated phagosomal lysis in a cellular model of infection. Thus, either EsxA is not required for phagosomal lysis, or additional ESX-1-associated proteins are required (182).…”

Virulence Factors and Pathogenicity of Mycobacterium

“…ESX-1 allows cytosolic contact and mediates vacuoles rupture [47]; the protein intervenes in host cell lysis in a contact dependent way, producing gross membrane disruptions [48]. DNA transfer through conjugation is also a function of ESX-1 system [49]; a phenomenon called "distributive conjugal transfer" that describes a genetic exchange between recipient and donor is dependent of ESX-1 in M. smegmatis [50].…”

“…NOX2 is a multiprotein enzyme complex that assembles and activated in response to phagocytosis. This enzyme complex transfers electrons across the membrane from cytosolic NADPH to molecular oxygen, the reaction produce superoxide anions (O 2 − ) which dismutates into hydrogen peroxide (H 2 O 2 ) and generates toxic hydroxyl radicals [48]. iNOS is induced upon IFN-γ activation and produces nitrite and nitrate via nitric oxide (NO), this reacts with O 2 − and forms peroxynitrite (OONO − ) [97].…”