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Identified virulence factors of Staphylococcus: Secretion system


Type VII secretion system  

Related genes: esaA; esaB; esaD; esaE; esaG1; esaG2; esaG3; esaG4; esaG5; esaG6; esaG7; esaG8; esaG9; essA; essB; essC; esxA; esxB; esxC; esxD;
Keywords: Secretion system; Type VII secretion system;
Characteristics:
At the molecular level, the S. aureus T7SS is composed of four membrane-associated proteins (EsaA, EssA, EssB, and EssC), three soluble cytosolic proteins (EsaB, EsaE, and EsaG), and five secreted virulence factors (EsxA, EsxC, EsxB, EsxD, and EsaD).
Figures:
The Staphylococcal Type VII Secretion System, Ess (From: Unnikrishnan M, et al., 2017. The Enigmatic Esx Proteins: Looking Beyond Mycobacteria. Trends Microbiol 25(3):192-204.).


Functions:
Plays a key role in promoting bacterial survival and the long-term persistence.
Play key roles in bacterial competitiveness.
Mechanism:
ESAT-6-like secretion system (Ess) encoded by a cluster of 12 genes in S. aureus. The FSD (FtsK/SpoIIIE domain) membrane protein EssC is essential for the secretion of EsxA-EsxB. EssA and EssB that encode transmembrane proteins are also involved in secretion. The secretion of EsxA is dependent on the presence of EsxB and vice versa. The co-dependence is similar to that of ESAT-6 and CFP-10 in M. tuberculosis. S. aureus mutants that fail to secrete EsxA and EsxB display significantly reduced virulence and are defective in dissemination and colonization..
S. aureus T7SS secretes a large nuclease toxin, EsaD. The toxic activity of EsaD is neutralised during its biosynthesis through complex formation with an antitoxin, EsaG, which binds to its C-terminal nuclease domain.
References:
Burts ML, et al., 2005. EsxA and EsxB are secreted by an ESAT-6-like system that is required for the pathogenesis of Staphylococcus aureus infections. Proc. Natl. Acad. Sci. USA. 102(4):1169-1174.
Cao Z, et al., 2016. The type VII secretion system of Staphylococcus aureus secretes a nuclease toxin that targets competitor bacteria. Nat Microbiol 2:16183.








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