title: A syringe-like injection mechanism in Photorhabdus luminescens toxins.
abstract: Photorhabdus luminescens is an insect pathogenic bacterium that is symbiotic with entomopathogenic nematodes. On invasion of insect larvae, P. luminescens is released from the nematodes and kills the insect through the action of a variety of virulence factors including large tripartite ABC-type toxin complexes (Tcs). Tcs are typically composed of TcA, TcB and TcC proteins and are biologically active only when complete. Functioning as ADP-ribosyltransferases, TcC proteins were identified as the actual functional components that induce actin-clustering, defects in phagocytosis and cell death. However, little is known about the translocation of TcC into the cell by the TcA and TcB components. Here we show that TcA in P. luminescens (TcdA1) forms a transmembrane pore and report its structure in the prepore and pore state determined by cryoelectron microscopy. We find that the TcdA1 prepore assembles as a pentamer forming an α-helical, vuvuzela-shaped channel less than 1.5 nanometres in diameter surrounded by a large outer shell. Membrane insertion is triggered not only at low pH as expected, but also at high pH, explaining Tc action directly through the midgut of insects. Comparisons with structures of the TcdA1 pore inserted into a membrane and in complex with TcdB2 and TccC3 reveal large conformational changes during membrane insertion, suggesting a novel syringe-like mechanism of protein translocation. Our results demonstrate how ABC-type toxin complexes bridge a membrane to insert their lethal components into the cytoplasm of the host cell. We believe that the proposed mechanism is characteristic of the whole ABC-type toxin family. This explanation of toxin translocation is a step towards understanding the host-pathogen interaction and the complex life cycle of P. luminescens and other pathogens, including human pathogenic bacteria, and serves as a strong foundation for the development of biopesticides.
authors.affiliation: Department of Physical Biochemistry, Max Planck Institute of Molecular Physiology, 44227 Dortmund, Germany.
authors.forename: Christos
authors.initials: C
authors.lastname: Gatsogiannis
authors.forename: Alexander E
authors.initials: AE
authors.lastname: Lang
authors.forename: Dominic
authors.initials: D
authors.lastname: Meusch
authors.forename: Vanda
authors.initials: V
authors.lastname: Pfaumann
authors.forename: Oliver
authors.initials: O
authors.lastname: Hofnagel
authors.forename: Roland
authors.initials: R
authors.lastname: Benz
authors.forename: Klaus
authors.initials: K
authors.lastname: Aktories
authors.forename: Stefan
authors.initials: S
authors.lastname: Raunser
mesh_terms: D036002:ADP Ribose Transferases / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure; D000818:Animals; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D001427:Bacterial Toxins / Q000737:chemistry / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D020285:Cryoelectron Microscopy; D003593:Cytoplasm / Q000378:metabolism; D054884:Host-Pathogen Interactions; D007313:Insecta / Q000166:cytology / Q000378:metabolism / Q000382:microbiology; D008954:Models, Biological; D008958:Models, Molecular; D020637:Photorhabdus / Q000378:metabolism* / Q000472:pathogenicity / Q000648:ultrastructure; D052899:Pore Forming Cytotoxic Proteins / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D011487:Protein Conformation; D021381:Protein Transport
chemical_list: D001426:Bacterial Proteins; D001427:Bacterial Toxins; D052899:Pore Forming Cytotoxic Proteins; D036002:ADP Ribose Transferases