PDBsum entry 2bk2

Toxin

PDB id: 2bk2

Contents

Protein chain

456 a.a.*

* C-alpha coords only

References listed in PDB file

Key reference

Title

Structural basis of pore formation by the bacterial toxin pneumolysin.

Authors

S.J.Tilley, E.V.Orlova, R.J.Gilbert, P.W.Andrew, H.R.Saibil.

Ref.

Cell, 2005, 121, 247-256. [DOI no: 10.1016/j.cell.2005.02.033]

PubMed id

15851031

Abstract

The bacterial toxin pneumolysin is released as a soluble monomer that kills target cells by assembling into large oligomeric rings and forming pores in cholesterol-containing membranes. Using cryo-EM and image processing, we have determined the structures of membrane-surface bound (prepore) and inserted-pore oligomer forms, providing a direct observation of the conformational transition into the pore form of a cholesterol-dependent cytolysin. In the pore structure, the domains of the monomer separate and double over into an arch, forming a wall sealing the bilayer around the pore. This transformation is accomplished by substantial refolding of two of the four protein domains along with deformation of the membrane. Extension of protein density into the bilayer supports earlier predictions that the protein inserts beta hairpins into the membrane. With an oligomer size of up to 44 subunits in the pore, this assembly creates a transmembrane channel 260 A in diameter lined by 176 beta strands.

Figure 2.
Figure 2. 3D Reconstructions of Prepore and Pore Forms of Pneumolysin

Figure 4.
Figure 4. Atomic Structure Fits of Prepore and Pore Structures

The above figures are reprinted by permission from Cell Press: Cell (2005, 121, 247-256) copyright 2005.

Secondary reference #1

Title

Structure of a cholesterol-Binding, Thiol-Activated cytolysin and a model of its membrane form.

Authors

J.Rossjohn, S.C.Feil, W.J.Mckinstry, R.K.Tweten, M.W.Parker.

Ref.

Cell, 1997, 89, 685-692. [DOI no: 10.1016/S0092-8674(00)80251-2]

PubMed id

9182756

Figure 3.
Figure 3. A Model for Membrane Insertion of Thiol-Activated Cytolysins as Suggested by the PFO Structure(A) Initial interaction with the target cell occurs with the PFO monomer being concentrated at the membrane surface by virtue of its binding to the membrane-bound receptor, cholesterol.(B) Large arc- and ring-shaped oligomers form on the membrane surface. The oligomers are activated with cholesterol molecules (indicated by dark blue spheres) binding in the Trp-464 pocket, causing displacement of the Trp-rich motif loop and formation of a hydrophobic dagger (see Figure 2B), which causes the oligomer to partition into the membrane. Because the aliphatic side chain of cholesterol is likely buried toward the center of the bilayer, cholesterol binding would also help to draw the toxin into the bilayer.(C) The inserted oligomer forms a pore. The charged face of Domain 4 contributes to the water-filled pore, and the other face (see Figure 5A) forms an extended β sheet structure that packs against the hydrophobic core of the membrane via clusters of cholesterol molecules. All of these pictures were generated with the program MidasPlus ( [18]).

Figure 5.
Figure 5. Views of the Surface of Domain 4(A) The opposite face to the conserved Trp-rich motif.(B) Domain 4 loops. Residues are colored according to their charge: red is negatively charged, blue is positively charged, cyan is polar, and green is nonpolar. These figures were generated using MidasPlus ([18]).

The above figures are reproduced from the cited reference with permission from Cell Press