Biophysical Society Thematic Meeting - October 13-15, 2015

Biophysics of Proteins at Surfaces: Assembly, Activation, Signaling

Tuesday Speaker Abstracts

Surface Induced Oligomerisation--the Case of the Alpha-Toxin from S.aureus Nadja Hellmann , Markus Schwiering. University of Mainz, Mainz, Germany. Pore forming toxins can be found in many organisms from different taxa. Frequently the toxin is a protein, which is secreted as a monomer, binds to the membrane and undergoes a conformational towards a membrane-spanning pore. The alpha-toxin from S.aureus (Hla) is able to lyse pure lipid membranes. We investigated the influence of the lipid membrane composition on the oligomerisation level by employing fluorescence spectroscopy of pyren-labelled toxin, SDS-gelelectrophoresis and fluorescence microscopy in order to find out whether the toxin has a preference for regions with particular Lipid composition. Increasing concentration of cholesterol and sphingomyelin (compared to phosphatidylcholine) facilitate oligomer formation and lysis in phase separating lipid mixtures. On the first glance this seems to indicate, that a preference for raft-structures exists.However, substitution of saturated SM by unsaturated SM (OSM=oleoyl SM) showed that the fluid disordered phase in particular enhances oligomerisation [1]. Taken together, these results indicate that this toxin tends to interact with or accumulate in the liquid disordered phase rather than the liquid ordered phase. This is supported by fluorescence microscopy. Simulations in comparison with experimental data indicate that oligomerisation probability rather than monomer binding affinity is enhanced by presence of SM. Thus, in contrast to some other pore forming toxins the preference for SM-containing lipid membranes seems to be not a consequence of specific interaction of the lipid binding pocket of the toxin. Possibly binding to SM keeps the toxin monomers in an orientation more suitable for oligomerisation. This work was supported by the DFG (SFB 490). [1] Schwiering, M., A. Brack, et al. (2013). "Lipid and phase specificity of alpha-toxin from S. aureus." Biochim Biophys Acta 1828(8): 1962-72.

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