Architecture of a bacterial type II secretion system

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Authors: Anastasia A Chernyatina and Harry H Low. bioRxiv preprint first posted online Aug. 22, 2018.

COMMENT: In this Preprint the authors, using a fusion of negative stain and cryo-electron microscopy (EM), reveal the core architecture of an assembled T2SS (Type II Secretion Systems) from the pathogen Klebsiella pneumoniae.

Human pathogenic bacteria such as Acinetobacter baumannii, Chlamydia trachomatis, Escherichia coli and Vibrio cholerae harbor Type II Secretion Systems (T2SS) in their genomes. This type of secretion system secretes digestive enzymes and toxins as the cholera toxin and other heat-labile toxins. To solve its structure is hence a very relevant advance.

Here we isolate an assembled T2SS so that both OM (Outer Membrane) and IM (Inner Membrane) components are captured together. Using a fusion of cryo and negative stain EM, combined with stoichiometry measurements, we provide a reconstruction of the entire OMC (Outer Membrane Complex) and a model for the cytoplasmic

components of the AP (Assembly Platform). Combined they reveal the core ultrastructure of this cell envelope spanning nanomachine.

......our results reveal the ultrastructure of an assembled T2SS and show the core architecture to be different to other known secretion systems

The atomic coordinates of the T2SS solved structure have been deposited in the Protein Data Bank (PDB) under accession code 6HCG.

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Raquel Tobes