PT - JOURNAL ARTICLE AU - Debnath Ghosal AU - Yi-Wei Chang AU - Kwang Cheol Jeong AU - Joseph P. Vogel AU - Grant J. Jensen TI - Molecular architecture of the <em>Legionella</em> Dot/Icm type IV secretion system AID - 10.1101/312009 DP - 2018 Jan 01 TA - bioRxiv PG - 312009 4099 - http://biorxiv.org/content/early/2018/05/01/312009.short 4100 - http://biorxiv.org/content/early/2018/05/01/312009.full AB - Legionella pneumophila survives and replicates inside host cells by secreting ~300 effectors through the Dot/Icm type IVB secretion system (T4BSS). Understanding this machine’s structure is challenging because of its large number of components (27) and integration into all layers of the cell envelope. Previously we overcame this obstacle by imaging the Dot/Icm T4BSS in its native state within intact cells through electron cryotomography. Here we extend our observations by imaging a stabilized mutant that yielded a higher resolution map. We describe for the first time the presence of a well-ordered central channel that opens up into a windowed large (~32 nm wide) secretion chamber with an unusual 13-fold symmetry. We then dissect the complex by matching proteins to densities for many components, including all those with periplasmic domains. The placement of known and predicted structures of individual proteins into the map reveals the architecture of the T4BSS and provides a roadmap for further investigation of this amazing specialized secretion system.