Oral Presentation The 4th Prato Conference on Pore Forming Proteins 2018

Membrane insertion of α-xenorhabdolysin in near-atomic detail (#57)

Evelyn Schubert 1 , Ingrid R Vetter 2 , Daniel Prumbaum 1 , Pawel A Penczek 3 , Stefan Raunser 1
  1. Department of Structural Biochemistry, Max Planck Institute of Molecular Physiology, 44227 Dortmund, Germany
  2. Department of Mechanistic Cell Biology, Max Planck Institute of Molecular Physiology, 44227 Dortmund, Germany
  3. Department of Biochemistry and Molecular Biology, The University of Texas, Houston Medical School, Houston, Texas 77030, USA

Pore-forming toxins (PFTs) are soluble proteins produced by bacteria and higher eukaryotes, that spontaneously form pores in biomembranes and act as toxins [1]. Dependent on their transmembrane region, which is formed either by α-helices or β-strands, PFTs are classified as α-PFTs and β-PFTs [2], [3]. A common trait of all PFTs is the conversion from a soluble monomer to a membrane-embedded oligomer [3]. α-Xenorhabdolysins (Xax) are α-pore-forming toxins (α-PFT) that form 1-1.3 MDa large pore complexes to perforate the host cell membrane. PFTs are used by a variety of bacterial pathogens to attack host cells. Xax has been first isolated from the bacterium Xenorhabdus nematophila [4]. Xenorhabdolysins are also found in other entomopathogenic bacteria, such as Photorhabdus luminescens, and human pathogenic bacteria, such as Yersinia enterocolitica and Proteus mirabilis [5, 6].They are composed of two subunits, namely XaxA (45 kDa) and XaxB (40 kDa) and are only active when the two components act together [5]. Due to the lack of structural information, the molecular mechanism of action of Xax toxins is poorly understood. Here, we report the cryo-EM structure of the XaxAB pore complex from Xenorhabdus nematophila and the crystal structures of the soluble monomers of XaxA and XaxB. The structures reveal that XaxA and XaxB are built similarly and appear as heterodimers in the 12-15 subunits containing pore, classifying XaxAB as bi-component α-PFT. Major conformational changes in XaxB, including the swinging out of an amphipathic helix are responsible for membrane insertion. XaxA acts as an activator and stabilizer for XaxB that forms the actual transmembrane pore. Based on our results, we propose a novel structural model for the mechanism of Xax intoxication.

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