ESAT-6 is a small protein appears to be of fundamental importance in virulence and protective immunity in Mycobacterium tuberculosis. Homologues have been detected in other Gram-positive bacterial species. It may represent a novel secretion system potentially driven by the Pfam:PF01580 domains in the YukA-like proteins [1].

1: The ESAT-6/WXG100 superfamily -- and a new Gram-positive secretion system?. Pallen MJ; Trends Microbiol 2002;10:209-212. PMID:11973144

2: EsxA and EsxB are secreted by an ESAT-6-like system that is required for the pathogenesis of Staphylococcus aureus infections. Burts ML, Williams WA, DeBord K, Missiakas DM; Proc Natl Acad Sci U S A. 2005;102:1169-1174. PMID:15657139

3: Outer membrane translocation: numerical protein secretion nomenclature in question in mycobacteria. Desvaux M, Hebraud M, Talon R, Henderson IR; Trends Microbiol. 2009;17:338-340. PMID:19674902

4: New insights into the distribution of WXG100 protein secretion systems. Sutcliffe IC; Antonie Van Leeuwenhoek. 2011;99:127-131. PMID:20852931

5: Secretion and subcellular localizations of bacterial proteins: a semantic awareness issue. Desvaux M, Hebraud M, Talon R, Henderson IR; Trends Microbiol. 2009;17:139-145. PMID:19299134