Molecular architecture, polar targeting and biogenesis of the Legionella Dot/Icm T4SS

• Published in: Nature microbiology Vol. 4; no. 7; pp. 1173 - 1182
• Main Authors: Ghosal, Debnath, Jeong, Kwangcheol C., Chang, Yi-Wei, Gyore, Jacob, Teng, Lin, Gardner, Adam, Vogel, Joseph P., Jensen, Grant J.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.07.2019; Nature Publishing Group
• Subjects: 631/326/41/2180; 631/326/41/2536; 631/535/1258/1260; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Biomedical and Life Sciences; Biosynthesis; Cell Membrane - chemistry; Cell Membrane - ultrastructure; Cell Polarity; Electron Microscope Tomography; Immunofluorescence; Infectious Diseases; Legionella; Legionella pneumophila - chemistry; Legionella pneumophila - cytology; Legionella pneumophila - genetics; Legionella pneumophila - ultrastructure; Life Sciences; Medical Microbiology; Microbiology; Microscopy; Microscopy, Fluorescence; Mutation; Parasitology; Periplasm - chemistry; Periplasm - ultrastructure; Protein Multimerization; Type IV Secretion Systems - chemistry; Type IV Secretion Systems - metabolism; Type IV Secretion Systems - ultrastructure; Virology
• ISSN: 2058-5276; 2058-5276
• DOI: 10.1038/s41564-019-0427-4

Legionella pneumophila survives and replicates inside host cells by secreting ~300 effectors through the defective in organelle trafficking (Dot)/intracellular multiplication (Icm) type IVB secretion system (T4BSS). Here, we used complementary electron cryotomography and immunofluorescence microscopy to investigate the molecular architecture and biogenesis of the Dot/Icm secretion apparatus. Electron cryotomography mapped the location of the core and accessory components of the Legionella core transmembrane subcomplex, revealing a well-ordered central channel that opens into a large, windowed secretion chamber with an unusual 13-fold symmetry. Immunofluorescence microscopy deciphered an early-stage assembly process that begins with the targeting of Dot/Icm components to the bacterial poles. Polar targeting of this T4BSS is mediated by two Dot/Icm proteins, DotU and IcmF, that, interestingly, are homologues of the T6SS membrane complex components TssL and TssM, suggesting that the Dot/Icm T4BSS is a hybrid system. Together, these results revealed that the Dot/Icm complex assembles in an ‘axial-to-peripheral’ pattern. A combination of electron cryotomography and immunofluorescence microscopy reveals the structure of the core transmembrane subcomplex of the Legionella defective in organelle trafficking (Dot)/intracellular multiplication (Icm) type IVB secretion system (T4BSS) and an early-stage assembly process by which T4BSS components are targeted to the bacterial poles by DotU and IcmF.