Molecular Determinants of effective Pore Formation

Abstract

Although the alpha-toxin from S. aureus was the first pore-forming toxin identified, its mode of interaction with membranes is still not fully understood. The toxin forms heptameric pores on cellular and artificial membranes. The observation that artificial membranes are permeabelized by this toxin indicates that no protein receptor is mandatory. Efficient permeabilisation is only possible in presence of cholesterol and sphingomyelin, which could be interpreted as a preference of the toxin for raft-like structures. However, variation of lipid composition and determination of oligomer formation by pyrene-fluorescence reveals, that the toxin favors specifically sphingomyelin in combination with cholesterol and that the interaction is not raft-specific in a general sense. The mode of action seems also to differ from the primary binding of the toxin lysenin, which binds specifically to sphingomyelin. Under certain conditions also non-lytic oligomers can be formed, for example at low temperatures or for certain mutants. The spectra obtained for pyrenelabelled mutants indicate that also lipid-composition might modulate the probability of lytic versus non-lytic pore formation, which might give a hint why for some cell non-lytic cells are found. Employing both AFM and fluorescence microscopy we aim to determine the molecular basis for efficient pore formation by this toxin. We thank the DFG (SFB 490) for financial support, S.Bhakdi and A.Valeva for production of the toxin and helpful discussions, G. Gimpl for help with fluorescence microscopy and the MPI for Polymer Research for the possibility to use the AFM.