Modeling the bacterial protein toxin, pneumolysin, in its monomeric and oligomeric form.

P J Morgan,S C Hyman,O Byron,P W Andrew,T J Mitchell,A J Rowe

doi:10.1016/s0021-9258(18)47249-3

Abstract

Pneumolysin is a member of the family of related bacterial thiol-activated toxins, which share structural similarities and a proposed common cytolytic mechanism. Currently the molecular mechanism of membrane damage caused by these toxins remains a matter of controversy. A prerequisite for defining this mechanism is a detailed knowledge of the monomeric and oligomeric pneumolysin structures. We present for the first time details of the monomeric structure of a thiol-activated toxin, pneumolysin. Electron microscope images of metal-shadowed pneumolysin monomers show an asymmetric molecule composed of four domains. We have studied the conformation of pneumolysin monomer by low resolution hydrodynamic bead modeling procedures. The bead model dimensions and shape are derived solely from the electron micrographs. The bead model has been evaluated in terms of the predicted solution properties, which in turn have been compared to the experimental values of the sedimentation coefficient, s(20,w)0, obtained by analytical ultracentrifugation and the intrinsic viscosity, [eta]. Pneumolysin oligomers, observed as ring- and arc-shaped structures, were also examined by electron microscopy. Metal shadowing and negative staining methods were used to establish the overall dimensions of the oligomer and were used to produce a morphological model for the oligomer, incorporating monomer subunits based on the hydrodynamic bead model.

Highlights

Pneumolysinis a member of the family of related baca-nd resulting oligomerization of toxin monomers in the memterialthiol-activatedtoxins,whichsharestructural brane (Bhakdi et al, 1985)
The bead model has been evaluated in terms of obtained by use of electron microscopy techniques
The same the predicted solution properties, which in turn have techniques have been applied to the pneumolysin monomer, been compared to the experimental values of the sedi- and based on these studies we are able to proposae hydrodymentation coefficients&, obtained by analytical ultra- namic bead model for the monomer structure

Summary

Introduction

Pneumolysinis a member of the family of related baca-nd resulting oligomerization of toxin monomers in the memterialthiol-activatedtoxins,whichsharestructural brane (Bhakdi et al, 1985). The same the predicted solution properties, which in turn have techniques have been applied to the pneumolysin monomer, been compared to the experimental values of the sedi- and based on these studies we are able to proposae hydrodymentation coefficients&,,,, obtained by analytical ultra- namic bead model for the monomer structure. 1994)to show that pneumolysin forms thr sodiumphosphotungstaterevealedringandarcstructures identical to those seen in membranes (Fig. 2).

Results

Conclusion