Structural basis for self-assembly of a cytolytic pore lined by protein and lipid.

Koji Tanaka,Koldo Morante,Jose M.M Caaveiro,Juan Manuel González-Mañas,Kouhei Tsumoto

doi:10.1038/ncomms7337

Koji Tanaka, Koldo Morante + Show 3 more

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https://doi.org/10.1038/ncomms7337

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Abstract

Pore-forming toxins (PFT) are water-soluble proteins that possess the remarkable ability to self-assemble on the membrane of target cells, where they form pores causing cell damage. Here, we elucidate the mechanism of action of the haemolytic protein fragaceatoxin C (FraC), a α-barrel PFT, by determining the crystal structures of FraC at four different stages of the lytic mechanism, namely the water-soluble state, the monomeric lipid-bound form, an assembly intermediate and the fully assembled transmembrane pore. The structure of the transmembrane pore exhibits a unique architecture composed of both protein and lipids, with some of the lipids lining the pore wall, acting as assembly cofactors. The pore also exhibits lateral fenestrations that expose the hydrophobic core of the membrane to the aqueous environment. The incorporation of lipids from the target membrane within the structure of the pore provides a membrane-specific trigger for the activation of a haemolytic toxin.

Highlights

Pore-forming toxins (PFT) are water-soluble proteins that possess the remarkable ability to self-assemble on the membrane of target cells, where they form pores causing cell damage
Actinoporins are classified as a-helical PFT (a-PFT) because the transmembrane pore is predicted to form an a-helical barrel[12,13]
The structure of the transmembrane pore of actinoporins was studied with electron microscopy (EM), yielding two contrasting models—a 9-mer ahelical-bundle pore[17], and a tetrameric toroidal pore formed by non-interacting proteins glued together by lipids from the membrane[18]

Summary

Introduction

Pore-forming toxins (PFT) are water-soluble proteins that possess the remarkable ability to self-assemble on the membrane of target cells, where they form pores causing cell damage. PFT are water-soluble proteins with the remarkable ability to spontaneously self-assemble into transmembrane pores on the lipid membrane of the target cell, causing cell-damage[3,4]. We reveal structures of FraC corresponding to four different stages of its activation route, namely the water-soluble form, the lipid-bound form, an assembly intermediate and the transmembrane pore. We provide a detailed account of the activation of a a-PFT at the atomic level These data clarify key aspects of the mechanism of action of actinoporins, and reveal critical roles for lipids in the activation and architecture of a PFT

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