RT Journal Article SR Electronic T1 Structure and dynamics of the ESX-5 type VII secretion system of Mycobacterium tuberculosis JF bioRxiv FD Cold Spring Harbor Laboratory SP 2020.12.02.408906 DO 10.1101/2020.12.02.408906 A1 Catalin M. Bunduc A1 Dirk Fahrenkamp A1 Jiri Wald A1 Roy Ummels A1 Wilbert Bitter A1 Edith N.G. Houben A1 Thomas C. Marlovits YR 2020 UL http://biorxiv.org/content/early/2020/12/02/2020.12.02.408906.abstract AB Mycobacterium tuberculosis causes one of the most important infectious diseases in humans, leading to 1.5 million deaths every year. Specialized protein transport systems, called type VII secretion systems (T7SSs), are central for its virulence, but also crucial for nutrient and metabolite transport across the mycobacterial cell envelope. Here we present the first structure of an intact T7SS inner membrane complex of M. tuberculosis. We show how the 2.32 MDa, 165 transmembrane helices-containing ESX-5 assembly is restructured and stabilized as a trimer of dimers by the MycP5 protease. A trimer of MycP5 caps a central periplasmic dome-like chamber formed by three EccB5 dimers, with the proteolytic sites facing towards the cavity. This chamber suggests a central secretion and processing conduit. Complexes without MycP5 show disruption of the EccB5 periplasmic assembly and increased flexibility, highlighting the importance of this component for complex integrity. Beneath the EccB5-MycP5 chamber, dimers of the EccC5 ATPase assemble into three four-transmembrane helix bundles, which together seal the potential central secretion channel. Individual cytoplasmic EccC5 domains adopt two distinctive conformations, likely reflecting different secretion states. Our work suggests a novel mechanism of protein transport and provides a structural scaffold to aid drug development against the major human pathogen.Competing Interest StatementThe authors have declared no competing interest.