M. tuberculosis esxA

A secreted protein that plays a number of roles in modulating the host's immune response to infection as well as being responsible for bacterial escape into the host cytoplasm. Acts as a strong host (human) T-cell antigen.

ESAT-6 protein EsxA

A secreted protein that plays a number of roles in modulating the host's immune response to infection as well as being responsible for bacterial escape into the host cytoplasm. Acts as a strong host (human) T-cell antigen (PubMed:7729876, PubMed:11940590).
Inhibits IL-12 p40 (IL12B) and TNF-alpha expression by infected host (mouse) macrophages, reduces the nitric oxide response by about 75% (PubMed:14557536).
In mice previously exposed to the bacterium, elicits high level of IFN-gamma production by T-cells upon subsequent challenge by M.tuberculosis, in the first phase of a protective immune response (PubMed:7897219, PubMed:7729876).
Higher levels (1.6-3.3 uM) of recombinant protein inhibit IFN-gamma production by host (human) T-cells and also IL-17 and TNF-alpha production but not IL-2; decreases expression of host ATF-2 and JUN transcription factors by affecting T-cell receptors signaling downstream of ZAP70, without cytotoxicity or apoptosis (PubMed:19265145).
EsxA inhibits IFN-gamma production in human T-cells by activating p38 MAPK (MAPK14), p38 MAPK is not responsible for IL-17 decrease (PubMed:21586573).
Binds host (mouse) Toll-like receptor 2 (TLR2) and decreases host MYD88-dependent signaling; binding to TLR2 activates host kinase AKT and subsequently inhibits downstream activation of NF-kappa-B; the C-terminal 20 residues (76-95) are necessary and sufficient for the TLR2 inhibitory effect (PubMed:17486091).
Required for induction of host (human) IL-1B maturation and release by activating the host NLRP3/ASC inflammasome; may also promote access of other tuberculosis proteins to the host cells cytoplasm (PubMed:20148899).
Induces IL-8 (CXCL8) expression in host (human) lung epithelial cells (PubMed:23867456).
Exogenously applied protein, or protein expressed in host (human and mouse), binds beta-2-microglobulin (B2M) and decreases its export to the cell surface, probably leading to defects in class I antigen presentation by the host cell (PubMed:25356553).
Responsible for mitochondrial fragmention, redistribution around the cell nucleus and decreased mitochondrial mass; this effect is not seen until 48 hours post-infection (PubMed:26092385).
Able to disrupt artificial planar bilayers in the absence of EsxB (CFP-10) (PubMed:14557547).
Native protein binds artificial liposomes in the absence but not presence of EsxB and is able to rigidify and lyse them; the EsxA-EsxB complex dissociates at acidic pH, EsxB might serve as a chaperone to prevent membrane lysis (PubMed:17557817).
Recombinant protein induces leakage of phosphocholine liposomes at acidic pH in the absence of ExsB, undergoes conformational change, becoming more alpha-helical at acidic pH (PubMed:23150662, PubMed:25645924).
The study using recombinant protein did not find dissociation of EsxA-EsxB complex at acidic pH (PubMed:23150662).
Involved in translocation of bacteria from the host (human) phagolysosome to the host cytoplasm (PubMed:17604718, PubMed:22319448).
Translocation into host cytoplasm is visible 3 days post-infection using cultured human cells and precedes host cell death (PubMed:22319448).
Recombinant protein induces apoptosis in host (human) differentiated cell lines, which is cell-line dependent; bacteria missing the ESX-1 locus do not induce apoptosis (PubMed:17298391).
Host (human) cells treated with EsxA become permeable to extracellular dye (PubMed:17298391).
EsxA and EsxA-EsxB are cytotoxic to pneumocytes (PubMed:19906174).
ESX-1 secretion system-induced host (mouse) cell apoptosis, which is probably responsible for infection of new host cells, might be due to EsxA (PubMed:23848406).
EsxA induces necrosis in aged neutrophils (PubMed:25321481).
May help regulate assembly and function of the type VII secretion system (T7SS) (By similarity).
EsxA disassembles pre-formed EccC-EsxB multimers, possibly by making EccC-EsxA-EsxB trimers instead of EccC-EsxB-EsxB-EccC tetramers. (By similarity)
May be critical in pro-bacteria versus pro-host interactions; ESX-1 mediates DNA mediated export (maybe via EsxA). The DNA interacts with host (human) cGAS, leading to cGAMP production and activation of the host STING-TBK-1-IRF-3 signaling pathway that leads to IFN-beta which is thought to be 'pro-bacteria'. Mycobacterial dsDNA also interacts with AIM2-NLRP3-ASC to activate an inflammasome, leading to the 'pro-host' IL-1-beta (PubMed:26048138, PubMed:26048136).

Modulation by symbiont of host signal transduction pathwayManual Assertion Based On ExperimentIDA:MTBBASE
Protein secretion by the type VII secretion systemManual Assertion Based On ExperimentIMP:MTBBASE
Suppression by symbiont of host cell-mediated immune responseManual Assertion Based On ExperimentIDA:MTBBASE
Suppression by symbiont of host T-cell mediated immune responseManual Assertion Based On ExperimentIDA:CACAO

Secreted
Secreted, cell wall
Host cell surface
Host cytoplasm
Host endoplasmic reticulum
Host cell membrane
Probably secreted via the ESX-1 / type VII secretion system (T7SS) (PubMed:19876390).
Secreted protein binds to bacterial cell wall (PubMed:19906174).
Binds to host (mouse) TLR2 on the cell surface (PubMed:17486091).
Binds to CD4+, CD8+, CD14+ and CD19+ host (human) cells (PubMed:19265145).
Localized on the cell surface of host (human) cell monocytes and macrophages (often in patches), but not fibroblasts (PubMed:15973432).
Exogenous EsxA and EsxA-EsxB complex can enter host (human and mouse) endoplasmic reticulum, where they bind beta-2-microglobulin (PubMed:25356553).
At acidic pH able to form pores in artificial membranes, might form pores in host phagosome membranes in absence of EsxB, allowing escape of bacteria into the host cytoplasm (PubMed:25645924, PubMed:26801203).
The central pair of alpha helices probably insert into the membrane while the N- and C-terminal arms do not, but may rest on the membrane surface as they are required for membrane insertion (PubMed:25645924).

Upon purification from strain ATCC 27294 a C-terminally truncated peptide (missing residues 85-95) has been found; it is not clear if this is physiologically relevant (PubMed:15378760).
An additional unknown modification on peptide Thr-86-Ala-95 has also been seen (PubMed:15378760).