title: Discovery of the type VII ESX-1 secretion needle?
abstract: Mycobacterium tuberculosis, the etiological agent of human tuberculosis, harbours five ESAT-6/type VII secretion (ESX/T7S) systems. The first esx gene clusters were identified during the genome-sequencing project of M. tuberculosis H37Rv. Follow-up studies revealed additional genes playing important roles in ESX/T7S systems. Among the latter genes, one can find those that encode Pro-Glu (PE) and Pro-Pro-Glu (PPE) proteins as well as a gene cluster that is encoded >260 kb upstream of the esx-1 locus and encodes ESX-1 secretion-associated proteins EspA (Rv3616c), EspC (Rv3615c) and EspD (Rv3614c). The espACD cluster has been suggested to have an important function in ESX-1 secretion since EspA-EspC and EsxA-EsxB are mutually co-dependent on each other for secretion. However, the molecular mechanism of this co-dependence and interaction between the substrates remained unknown. In this issue of Molecular Microbiology, Lou and colleagues show that EspC forms high-molecular weight polymerization complexes that resemble selected components of type II, III and/or IV secretion systems of Gram-negative bacteria. Indeed, EspC-multimeric complexes form filamentous structures that could well represent a secretion needle of ESX-1 type VII secretion systems. This exciting observation opens new avenues for research to discover and characterize ESX/T7S components and elucidates the co-dependence of EsxA/B secretion with EspA/C.
authors.affiliation: Institut Pasteur, Unit for Integrated Mycobacterial Pathogenomics, 75724 Paris Cedex 15, France.
authors.forename: Louis S
authors.initials: LS
authors.lastname: Ates
authors.affiliation: Institut Pasteur, Unit for Integrated Mycobacterial Pathogenomics, 75724 Paris Cedex 15, France.
authors.forename: Roland
authors.initials: R
authors.lastname: Brosch
mesh_terms: D000942:Antigens, Bacterial / Q000378:metabolism; D001426:Bacterial Proteins / Q000378:metabolism; D058947:Bacterial Secretion Systems / Q000235:genetics / Q000378:metabolism; D016680:Genome, Bacterial; D005810:Multigene Family; D009169:Mycobacterium tuberculosis / Q000235:genetics; D021381:Protein Transport; D000069377:Type VII Secretion Systems / Q000235:genetics / Q000378:metabolism
chemical_list: D000942:Antigens, Bacterial; D001426:Bacterial Proteins; D058947:Bacterial Secretion Systems; D000069377:Type VII Secretion Systems