Poster Presentation The 43rd Lorne Conference on Protein Structure and Function 2018

Cryo-EM structures of an ABC toxin complex in different states provide new clues to the mechanism of action (#219)

Sarah Piper 1 , Lou Brillault 1 , Joseph Box 1 , Tristan Croll 2 , Sebastian Scherer 3 , Kenneth Goldie 3 , Henning Stahlberg 3 , Mark Hurst 4 , Michael Landsberg 1
  1. University of Queensland, Brisbane, QLD, Australia
  2. Cambridge Institute for Medical Research, University of Cambridge, Cambridge, United Kingdom
  3. Biozentrum Basel, Basel, Switzerland
  4. AgResearch, Christchurch, New Zealand

ABC toxins are tripartite, pore-forming toxins of ~2 MDa in size that are found in a range of bacterial pathogens of insects and humans. The A subunit perforates cell membranes, enabling translocation of a cytotoxin (subunit C) and is strongly implicated in the specific recognition of host cell surfaces prior to (or upon) pore formation. It has remained unclear whether mechanisms of pore formation and cell surface recognition are shared across the ABC toxin family. Here we present cryo-EM structures of the Yersinia entomophaga type-II ABC toxin, YenTc, in the pre-pore form: First, a 6.7 Å resolution map of the asymmetric wild type YenTc (subunits A, B and C) and second, a 4.4 Å resolution structure of the pentameric A subunit. We were able to show that YenTc is a pore-forming toxin and used in vitro and in silico analyses to find structural evidence supporting a conformational change from the soluble, pre-pore form to the pore form, which reflects the membrane-embedded conformation of the complex. Cryo-EM reconstruction of the YenTc pore form provides insights into the conformational changes that accompany membrane insertion: the protrusion of the central α-helical bundle (which represents the translocation pore) from the complex, such that it can insert into a lipid membrane, as well as rearrangement of domains implicated in cell surface recognition. Overall, our results suggest that while the structural basis of pore formation is conserved across ABC toxin subtypes, the motifs involved in cell surface recognition are diverse, and thus provide insight into the mechanisms that ABC toxin-producing bacteria utilise to target different hosts.