Stepwise Visualization of Membrane Pore Formation by Suilysin, a Bacterial Cholesterol-Dependent Cytolysin

Elife. 2014 Dec 2;3:e04247. doi: 10.7554/eLife.04247.

Abstract

Membrane attack complex/perforin/cholesterol-dependent cytolysin (MACPF/CDC) proteins constitute a major superfamily of pore-forming proteins that act as bacterial virulence factors and effectors in immune defence. Upon binding to the membrane, they convert from the soluble monomeric form to oligomeric, membrane-inserted pores. Using real-time atomic force microscopy (AFM), electron microscopy (EM), and atomic structure fitting, we have mapped the structure and assembly pathways of a bacterial CDC in unprecedented detail and accuracy, focussing on suilysin from Streptococcus suis. We show that suilysin assembly is a noncooperative process that is terminated before the protein inserts into the membrane. The resulting ring-shaped pores and kinetically trapped arc-shaped assemblies are all seen to perforate the membrane, as also visible by the ejection of its lipids. Membrane insertion requires a concerted conformational change of the monomeric subunits, with a marked expansion in pore diameter due to large changes in subunit structure and packing.

Keywords: S. suis; bacterial toxins; biophysics; cholesterol-dependent cytolysins; membrane pore formation; pore-forming proteins; structural biology.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cell Membrane / drug effects
  • Cell Membrane / metabolism*
  • Cell Membrane / ultrastructure
  • Cholesterol / metabolism*
  • Computer Systems
  • Cryoelectron Microscopy
  • Diffusion
  • Disulfides / metabolism
  • Hemolysin Proteins / metabolism*
  • Kinetics
  • Microscopy, Atomic Force
  • Models, Molecular
  • Negative Staining
  • Perforin / metabolism*
  • Pore Forming Cytotoxic Proteins / metabolism*
  • Protein Multimerization

Substances

  • Disulfides
  • Hemolysin Proteins
  • Pore Forming Cytotoxic Proteins
  • suilysin
  • Perforin
  • Cholesterol