A heterodimer of EsxA and EsxB is involved in sporulation and is secreted by a type VII secretion system in Streptomyces coelicolor

Roman, Sandra Akpe San; Facey, Paul D.; Fernández-Martínez, Lorena T.; Rodríguez, Cynthia; Vallin, Carlos; Sol, Ricardo Del; Dyson, Paul

doi:10.1099/mic.0.037069-0

Cited by 45 publications

(44 citation statements)

References 38 publications

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“…Early secretory antigen 6 kDa (ESX, or type VII) secretion systems are widespread in actinomycetes and Gram-positive bacteria and affect a range of bacterial processes including sporulation, conjugation, and cell wall stability (6)(7)(8)(9)(10). In two notorious human pathogens, Mycobacterium tuberculosis and Staphylococcus aureus, ESX secretion was found to be crucial for establishing and maintaining the infection (11)(12)(13)(14)(15).…”

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Dimer recognition and secretion by the ESX secretion system inBacillus subtilis

Sysoeva

Zepeda-Rivera

Huppert

2014

Proc. Natl. Acad. Sci. U.S.A.

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Protein secretion typically involves translocation of unfolded polypeptides or transport of monomeric folded proteins. Here we provide, to our knowledge, the first experimental evidence for secretion of an intact multimeric complex requiring a signal formed by both members of the complex. Using systematic mutagenesis of a substrate involved in early secretory antigen 6 kDa (ESX) secretion in Bacillus subtilis, we demonstrate that export of the substrate requires two independent motifs. Using mixed dimers, we show that these motifs must form a composite secretion signal in which one motif is contributed by each subunit of the dimer. Finally, through targeted crosslinking we show that the dimer formed in the cell is likely secreted as a single unit. We discuss implications of this substrate recognition mechanism for the biogenesis and quality control of secretion substrates and describe its likely conservation across ESX systems.WXG protein | type VII secretion system | protein translocation | YukE P rotein secretion is critical for protein targeting in any living cell and for its communication with the environment. Bacteria use a wide range of secretion mechanisms to export proteins out of the cytoplasm. Signals for secretion are most commonly primary amino acid sequences, but in some cases also may be formed through interacting surfaces of a substrate and its delivery effector. Some secretion systems unfold their substrates to translocate them across the membrane and cell wall. Other systems export folded proteins, sometimes in complex with bound cofactors. For example, the general secretory machinery (Sec) denatures the tertiary and secondary structure of its substrates to thread the polypeptide through the narrow opening of the integral membrane translocon complex, SecYEG (1). Type III secretion system (T3SS) machinery is thought to unfold the tertiary structure of its substrates, while preserving the secondary structure elements for the substrate recognition (2, 3). In contrast, the twin-arginine transport (Tat) system exports folded substrates (4) and is hypothesized to be able to translocate protein oligomers and complexes via a "hitchhiking" mechanism (5). Overall, these and other secretion types differ in the nature of substrate recognition signal and the mode of substrate translocation.Early secretory antigen 6 kDa (ESX, or type VII) secretion systems are widespread in actinomycetes and Gram-positive bacteria and affect a range of bacterial processes including sporulation, conjugation, and cell wall stability (6-10). In two notorious human pathogens, Mycobacterium tuberculosis and Staphylococcus aureus, ESX secretion was found to be crucial for establishing and maintaining the infection (11-15). Despite the importance of the ESX secretion for human health, the mechanism of this type of secretion is still largely unknown.Recent characterization of the ESX system in Bacillus subtilis confirmed that a functional system is encoded by the yuk/yue operon (16,17). Importantly, the B. subtilis system codes for a...

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confidence: 99%

Dimer recognition and secretion by the ESX secretion system inBacillus subtilis

Sysoeva

Zepeda-Rivera

Huppert

2014

Proc. Natl. Acad. Sci. U.S.A.

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“…"Type VII" secretion systems distantly related to mycobacterial ESX systems have been identified in numerous other Gram-positive bacteria (13)(14)(15)(16)(17). The protein components of type VII secretion systems differ considerably between bacterial species but generally include the following: (i) one or more small helical proteins of the WXG100 protein family (e.g., ESAT-6, YukE), (ii) an FtsK/SpoIII-type ATPase that is thought to drive protein secretion (e.g., EccC, YukB), and (iii) a multipass transmembrane protein that may form the pore of the translocon (e.g., EccD, YueB).…”

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Structure of a PE–PPE–EspG complex fromMycobacterium tuberculosisreveals molecular specificity of ESX protein secretion

Ekiert

Cox

2014

Proc. Natl. Acad. Sci. U.S.A.

105

131

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Nearly 10% of the coding capacity of the Mycobacterium tuberculosis genome is devoted to two highly expanded and enigmatic protein families called PE and PPE, some of which are important virulence/immunogenicity factors and are secreted during infection via a unique alternative secretory system termed "type VII." How PE-PPE proteins function during infection and how they are translocated to the bacterial surface through the five distinct type VII secretion systems [ESAT-6 secretion system (ESX)] of M. tuberculosis is poorly understood. Here, we report the crystal structure of a PE-PPE heterodimer bound to ESX secretion-associated protein G (EspG), which adopts a novel fold. This PE-PPE-EspG complex, along with structures of two additional EspGs, suggests that EspG acts as an adaptor that recognizes specific PE-PPE protein complexes via extensive interactions with PPE domains, and delivers them to ESX machinery for secretion. Surprisingly, secretion of most PE-PPE proteins in M. tuberculosis is likely mediated by EspG from the ESX-5 system, underscoring the importance of ESX-5 in mycobacterial pathogenesis. Moreover, our results indicate that PE-PPE domains function as cis-acting targeting sequences that are read out by EspGs, revealing the molecular specificity for secretion through distinct ESX pathways.tuberculosis | protein secretion | antigenic variation | virulence factor | host-pathogen interactions

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“…In mycobacterial pathogens the ESX-1 system likely promotes permeabilization of the phagosomal membrane allowing either the bacterial cell or bacterial products access to the cytosol of the macrophage (6)(7)(8)(9)(10). The ESX-1/Wss system is conserved and functional in nonpathogenic bacteria, where it promotes a range of activities, including conjugation (11)(12)(13)(14)(15)(16).…”

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A Novel ESX-1 Locus Reveals that Surface-Associated ESX-1 Substrates Mediate Virulence in Mycobacterium marinum

et al. 2014

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EsxA (ESAT-6) and EsxB (CFP-10) are virulence factors exported by the ESX-1 system in mycobacterial pathogens. In Mycobacterium marinum, an established model for ESX-1 secretion in Mycobacterium tuberculosis, genes required for ESX-1 export reside at the extended region of difference 1 (RD1) locus. In this study, a novel locus required for ESX-1 export in M. marinum was identified outside the RD1 locus. An M. marinum strain bearing a transposon-insertion between the MMAR_1663 and MMAR_1664 genes exhibited smooth-colony morphology, was deficient for ESX-1 export, was nonhemolytic, and was attenuated for virulence. Genetic complementation revealed a restoration of colony morphology and a partial restoration of virulence in cell culture models. Yet hemolysis and the export of ESX-1 substrates into the bacteriological medium in vitro as measured by both immunoblotting and quantitative proteomics were not restored. We show that genetic complementation of the transposon insertion strain partially restored the translocation of EsxA and EsxB to the mycobacterial cell surface. Our findings indicate that the export of EsxA and EsxB to the cell surface, rather than secretion into the bacteriological medium, correlates with virulence in M. marinum. Together, these findings not only expand the known genetic loci required for ESX-1 secretion in M. marinum but also provide an explanation for the observed disparity between in vitro ESX-1 export and virulence.T he ESAT-6 system-1 (ESX-1)/WXG-100 secretion system (Wss) is required for the virulence of both Gram-positive and mycobacterial pathogens (1-5). In mycobacterial pathogens the ESX-1 system likely promotes permeabilization of the phagosomal membrane allowing either the bacterial cell or bacterial products access to the cytosol of the macrophage (6-10). The ESX-1/Wss system is conserved and functional in nonpathogenic bacteria, where it promotes a range of activities, including conjugation (11-16).Protein substrates are translocated across the mycobacterial cytoplasmic membrane by the ESX-1 export system (3, 5). Several genes are required for protein translocation, disruption of which results in loss of substrate secretion into the bacteriological medium (culture supernatant) in vitro (3)(4)(5)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26). It is unknown how the protein substrates are secreted across the mycolate outer membrane (MOM) out of the mycobacterial cell or if the known ESX genes promote MOM translocation. Likewise, it is not clear if the ESX-1 substrates are true exoproteins (released from the cell) or extrinsically associated with the MOM and shed into the bacteriological medium (27-29). Indeed, in addition to the culture supernatant, ESX-1 substrates have been localized to the mycobacterial cell wall and associated with the surface of the mycobacterial cell (28-31). It is unclear which population of ESX-1 substrates mediates virulence. The active secretion of ESX-1 substrates into the phagosome or cytosol of the macrophage has not been routinely observed.In the human ...

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A heterodimer of EsxA and EsxB is involved in sporulation and is secreted by a type VII secretion system in Streptomyces coelicolor

Cited by 45 publications

References 38 publications

Dimer recognition and secretion by the ESX secretion system inBacillus subtilis

Dimer recognition and secretion by the ESX secretion system inBacillus subtilis

Structure of a PE–PPE–EspG complex fromMycobacterium tuberculosisreveals molecular specificity of ESX protein secretion

A Novel ESX-1 Locus Reveals that Surface-Associated ESX-1 Substrates Mediate Virulence in Mycobacterium marinum

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