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Publication Abstract from PubMed

Bacterial contact-dependent growth inhibition (CDI) systems use a type Vb secretion mechanism to export large CdiA toxins across the outer membrane by dedicated outer membrane transporters called CdiB. Here we report the first crystal structures of two CdiB transporters from Acinetobacter baumannii and Escherichia coli. CdiB transporters adopt a TpsB fold, containing a 16-stranded transmembrane beta-barrel connected to two periplasmic domains. The lumen of the CdiB pore is occluded by an N-terminal alpha-helix and the conserved extracellular loop 6; these two elements adopt different conformations in the structures. We identified a conserved DxxG motif located on strand beta1 that connects loop 6 through different networks of interactions. Structural modifications of DxxG induce rearrangement of extracellular loops and alter interactions with the N-terminal alpha-helix, preparing the system for alpha-helix ejection. Using structural biology, functional assays, and molecular dynamics simulations, we show how the barrel pore is primed for CdiA toxin secretion.

Structural insight into toxin secretion by contact dependent growth inhibition transporters.,Guerin J, Botos I, Zhang Z, Lundquist K, Gumbart JC, Buchanan SK Elife. 2020 Oct 22;9. pii: 58100. doi: 10.7554/eLife.58100. PMID:33089781^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.