Oral Presentation The 3rd Prato Conference on Pore Forming Proteins 2015

Cholesterol-dependent cytolysins: From water-soluble state to membrane pore (#15)

Michael Parker 1
  1. St Vincent's Institute of Medical Research, Fitzroy, VIC, Australia
 

The cholesterol-dependent cytolysins (CDCs) are one of the most widely distributed toxins known, having been identified in 5 different genera of Gram-positive bacteria. The CDCs exhibit a number of unique features amongst pore-forming toxins including an absolute dependence on the presence of cholesterol-rich membranes for their activity and the formation of oligomeric transmembrane pores greater than 150 Å in diameter. There are more than 20 members of the CDC family so far identified and there exists a high degree of sequence homology (40-70%) suggesting they all have similar activities and 3D structures. The first crystal structure of a CDC was that of perfringolysin O1 and most of our understanding of CDC function is based on studies of this toxin.2,3 We have subsequently determined structures of other family members that have confirmed that the 3D fold first seen in PFO is shared by all family members.4-6

We have now determined a number of new CDC structures which are providing valuable insights into the role of receptor binding, oligomerisation and images of the prepore (unpublished results). Functional studies have revealed that CDCs undergo a highly regulated stepwise process in assembling as a large membrane pore consisting of more than 30 monomers. Not only is the conversion from water-soluble monomer to pore highly complex, it is essential that the pore does not form prematurely otherwise the target cell won’t be successfully breached.7 The crystal structures of the water-soluble states of these toxins, together with cryo-electron microscopy, small angle X-ray scattering data, fluorescence spectroscopy and molecular dynamics simulations have proved very useful for modelling the transition from water-soluble monomer to membrane pore.

  1. Rossjohn, J. et al., (1997) Structure of a cholesterol-binding, thiol-activated cytolysin and a model of its membrane form. Cell 89, 685-692.
  2. Shatursky, O. et al., (1999) The mechanism of membrane insertion for a cholesterol-dependent cytolysin: a novel paradigm for pore-forming toxins. Cell 99, 293-299.
  3. Gilbert, R.J. et al., (1999) Two structural transitions in membrane pore formation by pneumolysin, the pore-forming toxin of Streptococcus pneumoniae. Cell 97, 647-655
  4. Polekhina, G. et al., (2005) Insights into the action of the superfamily of cholesterol-dependent cytolysins from studies of intermedilysin. Proc. Natl. Acad. Sci. USA 102, 600-605.
  5. Feil, S.C. et al., (2012) Structure of the lectin regulatory domain of the cholesterol-dependent cytolysin lectinolysin reveals the molecular basis for its Lewis antigen specificity. Structure 20, 248-258.
  6. Feil, S.C. et al., (2014) Structural studies of Streptococcus pyogenes streptolysin O provides insights into the early steps of membrane penetration. J. Mol. Biol. 426, 785-792.
  7. Wade, K.R. et al., (2015) The molecular elements that control the prepore to pore transition in the cholesterol-dependent cytolysins. Proc. Natl. Acad. Sci. USA, in press.